John  Sv/ett 


/ 


**• 


TEXT-BOOKS    OF    SCIENCE;.:;, 


Now  in  course  of  publication,   in  small  Svo.   each  ^okim",   coK<tainji['g'>t\  ' 
about  300  pages,  price  35.  6d.    botmd  in  cloth, 

A     SERIES     OF 

ELEMENTARY  "WORKS  ON  MECHANICAL  AND 
PHYSICAL    SCIENCE, 

FORMING    A   SERIES   OF 

TEXT-BOOKS    OF    SCIENCE 

ADAPTED    FOR    THE    USE    OF    ARTISANS    AND    OF   STUDENTS    IN 
PUBLIC   AND    OTHER   SCHOOLS. 

Edited  by  T.  M.  GOODEVE,  M.A. 

Lecturer  on  Applied  Mathematics  at  the  Royal  School  of  Mines,  and  formerly 
Professor  of  Natural  Philosophy  in  King's  College,  London. 


HTHE  Reports  of  the  Public  Schools  Commission  and  of  the  Schools 
Inquiry  Commission,  as  well  as  the  evidence  taken  before  several 
Parliamentary  Committees,  have  shown  that  there  is  still  a  want  of 
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plete,  to  serve  as  a  basis  for  the  sound  instruction  of  Artisans,  and  at  the 
same  time  sufficiently  popular  to  suit  the  capacities  of  beginners.  The 
foundation  of  the  WHITWORTH  SCHOLARSHIPS  is  in  itself  an  evidence 
of  the  recognition  of  that  want,  and  a  reason  for  the  production  of  a 
Series  of  Elementary  Scientific  Works  adapted  to  that  purpose. 

Messrs.  LONGMANS  and  Co.  have  accordingly  made  arrangements 
for  the  issue  of  a  Series  of  Elementary  Works  in  the  various  branches 
of  Mechanical  and  Physical  Science  suited  for  general  use  in  Schools, 
and  for  the  self-instruction  of  Working  Men. 


.•2         •..*;:  .••  i  ^Text-Books  of  Science. 


l'***  These  "book^  are  intended  to  serve  for  the  use  of  practical  men, 
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Artisans  to  become  Candidates  for  the  WHITWORTH  SCHOLARSHIPS. 

The  following  is  a  list  of  the  books  intended  for  early  publication 
in  the  Elementary  Series,  to  be  followed  by  others  on  other  branches 
of  Science  : — 

1.  TECHNICAL  ARITHMETIC   AND    MENSURATION. 

By  C.  W.   MERRIFIELD,   F.R.S.  Principal  of  the  Royal  School  of  Naval 
Architecture,  South  Kensington.  [In  the  Press. 

2.  ALGEBRA  AND   TRIGONOMETRY. 

By  the  Rev.  W.  N.  GRIFFIN,  B.D.  sometime   Fellow  of  St.  John's  College, 
Cambridge.  \.PubliSJied. 

3.  PLANE  AND   SOLID   GEOMETRY. 

By  the  Rev.   H.  W  WATSON,  formerly  Fellow  of  Trinity  College,  Cam 
bridge,  and  late  Assistant-Master  of  Harrow  School.  [/«  the  press. 


Text-Books  of  Science. 


4.  PRACTICAL  AND    DESCRIPTIVE   GEOMETRY,   AND    PRIN 

CIPLES   OF    MECHANICAL   DRAWING. 

By  C.  W.  MERRIFIELD,  F.R.S.  Principal  of  the  Royal  School  of  Naval 
Architecture,  South  Kensington. 

5.  PRINCIPLES   OF    MECHANICS. 

By  T.  M.  GOODEVE,  M.A.  Editor  of  the  Series. 

6.  THE   ELEMENTS   OF    MECHANISM, 

Designed  for  Students  of  Applied  Mechanics.  By  T.  M.  GOODEVE,  M.A. 
Editor  of  the  Series.  With  257  Figures  on  Wood.  [Published. 

7.  DESCRIPTIVE    MECHANISM, 

Including  Descriptions  of  the  Lathes,  Planing,  Slotting,  and  Shaping 
Machines,  and  the  mode  of  Handling  Work  in  the  Engineer's  Shop  and 
other  Workshops. 

By  C.  P.  B.  SHELLEY,  Civil  Engineer,  and  Professor  of  Manufacturing 
Art  and  Machinery  at  King's  College,  Londor 

8.  THEORY  OF    HEAT. 

By  J.  CLERK  MAXWELL,  M.A.  F.R.SS.  L.  &  E.  [In  the  press. 

9.  ECONOMICAL  APPLICATIONS   OF   HEAT, 

Including  Combustion,  Evaporation,  Furnaces,  Flues,  and  Boilers. 

By  C.  P.  B.  SHELLEY,  Civil  Engineer,  and  Professor  of  Manufacturing 
Art  and  Machinery  at  King's  College,  London. 

With  a  Chapter  on  the  Probable  Future  Development  of  the  Science  of  Heat,  by 
C.  WILLIAM  SIEMENS,  F.R.S. 

10.  THE   STEAM    ENGINE. 

By  T.  M.  GOODEVE,  M.A.  Editor  of  the  Series. 

11.  SOUND   AND    LIGHT. 

By  G.  G.  STOKES,  M.A.  D.C.L.  Fellow  of  Pembroke  College,  Cambridge  ; 
Lucasian  Professor  of  Mathematics  in  the  University  of  Cambridge  ;  amd 
Secretary  to  the  Royal  Society. 


Text-Books  of  Science. 


12.  ELECTRICITY  AND    MAGNETISM. 

By  FLEEMING  JENKIN,  F.R.SS.  L.  &  E.  Professor  of  Engineering  in  the 
University  of  Edinburgh.  \[In  the  press. 

13.  STRENGTH    OF    MATERIALS. 

By  the  Rev.  JOHN  F.  TWISDEN,  M.A.  Professor  of  Mathematics  in  the  Staff 
College  ;  Author  of  '  Elementary  Introduction  to  Practical  Mechanics';  and 

By  JOHN  ANDERSON,  C.E.  Superintendent  of  Machinery  at  the  Royal 
Arsenal,  Woolwich. 

14.  INTRODUCTION      TO     THE     STUDY     OF      INORGANIC 

CHEMISTRY. 

By  WILLIAM  ALLEN  MILLER,  M.D.  LL.D.  F.R.S.  late  Professor  of 
Chemistry  in  King's  College,  London  ;  Author  of  '  Elements  of  Chemistry, 
Theoretical  and  Practical.'  With  71  Figures  on  Wood.  {Published. 

15.  METALS,   THEIR   PROPERTIES   AND   TREATMENT. 

By  CHARLES  LOUDON  BLOXAM,  Professor  of  Chemistry  in  King's 
College,  London ;  Professor  of  Chemistry  in  the  Department  of  Artillery 
Studies,  and  in  the  Royal  Military  Academy,  Woolwich.  With  105 
Figures  on  Wood.  [Published. 

At  an  early  period  will  be  published 

A  SHORT  PRELIMINARY  DISSERTATION  ON  THE  STUDY 
OF  MECHANICAL  AND  PHYSICAL  SCIENCE  AND 
ITS  RELATION  TO  THE  STUDY  OF  MATHEMATICS. 

By  R.  B.  CLIFTON,  M.A.  Cantab,  et  Oxon.  F.R.S.  F.R.A.S.  Hon.  Fellow 
of  Wadham  College,  Oxford,  and  Professor  of  Experimental  Philosophy  in 
the  University  of  Oxford. 


Messrs.  LONGMANS  and  Co.  having  secured  the  co-operation  of 
some  of  the  most  eminent  Professors  of,  and  Writers  on,  the  various 
branches  of  Science  comprised  in  this  Series,  are  enabled  to  indulge  in 
the  confident  hope  of  producing  a  Series  which  shall  combine  practical 
utility  with  sound  theory. 

39  PATERNOSTER  Row  :  February  1871. 


London  :  LONGMANS  and  CO.   Paternoster  Row. 


TEXT-BOOKS     OF     SCIENCE 


ADAPTED      FOK      THE      USE      OF 


ARTISANS    AND    STUDENTS    IN    PUBLIC    AND    OTHER    SCHOOLS. 


METALS. 


LONDON  :     PRINTED     BY 

SPOTTISWOODE      AND      CO.,      NEW-STREET      SQUARE 
AND   PARLIAMENT   STREET 


METALS: 


THEIR 


PROPERTIES      AND      TREATMENT. 


BY 


CHARLES   LOUDON    BLOXAM, 

Professor  of  Practical  Chemistry  in  Kings  College,  Lone 
Professor    of   Chemistry    in    the    Royal   Military 
Academy    and   in    the    Department    of 
Artillery  Studies,  Woolwich. 


D.      APPLETON      AND      CO. 

NEW    YORK. 

1872. 


PREFACE. 


THE  following  treatise  has  been  written  for  the  Series 
of  Text-Books  of  Science  published  by  Messrs.  Long 
mans  and  Co.,  and  intended  for  the  use  of  Artisans 
and  Students  in  Public  and  other  Schools. 

Its  subject,  Metallurgy,  one  of  the  most  ancient  of 
the  Arts,  and  closely  connected  with  the  progress 
of  civilization,  has  attained  to  enormous  proportions. 
The  processes  followed  in  the  treatment  of  any  par 
ticular  metal,  or  of  its  ores,  are  varied  according  to 
local  circumstances  and  traditions ;  a  few  only,  of 
modern  origin,  having  been  devised  upon  scientific 
principles.  To  describe  these  processes,  with  all 
their  modifications,  would  require  several  large  vo 
lumes.  The  Author,  consulting  the  interests  of  those 
persons  for  whom  the  Text-Books  are  designed,  has 
endeavoured  to  give  such  a  description  of  the  mode 
of  dealing  with  the  useful  metals  as  shall  enable  the 
Chemical  principles  involved  to  be  clearly  understood, 
and  shall  prepare  the  reader  for  the  more  detailed 
descriptions  which  are  to  be  found  in  larger  works. 

WOOLWICH  : 

October  1870. 

541808 


CONTENTS. 


PAGES 

PROPERTIES      DISTINGUISHING      THE      USEFUL 

METALS,    AS   A  CLASS I -10 

Lustre,  Tenacity,  Malleability,  Ductility,  Specific  Gravity, 
Conducting  Power  for  Heat  and  Electricity,  Fusibility. 


IRON  AND   STEEL 11-103 

Useful  properties  of  Iron  j  nature  and  composition  of  its 
Ores.  Extraction  of  Iron  in  the  form  of  Cast  Iron ;  calcining 
trie  Ores  ;  smelting  in  the  Blast  Furnace  ;  chemical  changes 
which  take  place  in  the  Blast  Furnace  ;  use  of  Waste  Gases  ; 
composition  of  the  Slag.  Composition  and  properties  of 
Cast  Iron ;  grey,  mottled,  and  white  Cast  Iron  ;  quantity 
and  effect  of  their  impurities.  Remelting  of  Cast  Iron  in 
the  foundry.  Conversion  of  Cast  Iron  into  Wrought  or  Bar 
Iron.  The  process  of  Refining.  The  Puddling  Process. 
Piling  and  Rolling  the  Puddled  Iron.  Conversion  of  Pud 
dled  Bar  into  Merchant  and  Best  Bar.  Fibrous  and  Crys 
talline  Iron.  Cold-shortness  and  Red-shortness.  Steel ; 


viii  Contents. 

properties  which  distinguish  it  from  Iron.  Conversion  of 
Bar  Iron  into  Steel  by  Cementation.  Conversion  of  Blistered 
Steel  into  Tilted  or  Shear  Steel.  Conversion  of  Blistered 
Steel  into  Cast  .  Steel.  Production  of  Bessemer  Steel. 
Spiegel-eisen.  Steel  Rails.  Heaton's  process  for  convert 
ing  Cast  Iron  into  Steel.  Homogeneous  Iron.  Siemens' 
Cast  Steel.  Puddled  Steel.  Natural  or  German  Steel. 
Impurities  in  Steel.  Hardening,  Tempering,  and  Anneal 
ing  Steel.  Case-hardening.  Malleable  Cast  Iron.  Ex 
traction  of  Malleable  Iron  directly  from  the  Ore. 


COPPER       ....  ....          I 

Composition  of  the  Ores  of  Copper.  Extraction  of  Copper 
from  its  Ores.  Calcining  or  Roasting.  Melting  for  Coarse 
Metal.  Calcination  of  the  Coarse  Metal.  Melting  for  Fine 
Metal.  Roasting  the  Fine  Metal.  Refining  and  Toughening. 
Theory  of  Poling.  Extraction  of  Copper  from  the  bitumin 
ous  schists  of  Mansfeld.  Refining  Copper  in  the  German 
Hearth.  Various  descriptions  of  Commercial  Copper. 
Effect  of  the  presence  of  foreign  matters  upon  the  quality  of 
Copper. 


TIN 130-52 

Mechanical  preparation  of  Tin  Ores,  Calcining  or  Roasting 
the  Tin  Ore.  Washing  the  roasted  Tin  Ore.  Smelting  the 
prepared  Tin  Ore.  Refining  the  metallic  Tin.  Reduction 
of  stream  Tin  Ore  in  the  Blast  Furnace  or  Blowing-house. 
Treatment  of  Tin  Ores  containing  Wolfram.  Manufacture 
of  Tin  Plate.  Tin  Plate  Moireed.  Tinning  of  Copper. 
Alloys  of  Tin  and  Copper.  Speculum  Metal.  Bell-metal. 
Gun-metal.  Bronze.  Britannia-metal. 


Contents.  ix 


PAGES 


ZINC 153-75 

Ores  of  Zinc.  English  method  of  extracting  Zinc.  Extrac 
tion  of  Zinc  from  its  Ores  by  the  Belgian  process.  Silesian 
process  for  extracting  Zinc.  Rolling  of  Zinc  into  sheets. 
Galvanised  Iron.  Alloys  of  Zinc  and  Copper.  Brass. 
Muntz  Metal.  Aich  Metal.  Sterro-metal.  German  Silver. 


LEAD  ..........        175-206 

Ores  of  Lead.  Smelting  of  Galena  in  the  Reverberatory 
Furnace.  Smelting  of  Lead  Ore  in  the  Scotch  Furnace  or 
Ore-hearth.  Smelting  of  Slags,  &c.,  in  the  Slag-hearth. 
Richardson's  or  Economic©  Furnace.  Softening  of  Lead  in 
the  Calcining  or  Improving  Furnace.  Refining  of  Lead 
containing  Silver  by  Pattinson's  process.  Uses  of  Lead. 
Type-metal.  Shot.  Alloys  of  Lead  and  Tin.  Pewter. 
Solder.  Soldering.  Brazing.  Terne-plate. 


SILVER        .  ...          206-38 

Native  Silver.  Silver-glance.  Horn  Silver.  Extraction 
of  Silver  from  Lead  by  Cupellation.  English  and  German 
Cupellation  Furnaces.  Extraction  of  Silver  from  the  Ores 
of  Copper.  Extraction  of  Silver  from  the  Ore  by  melting 
with  Lead.  Amalgamation  process  for  the  extraction  of 
Silver  from  its  Ores.  Mexican  process  of  amalgamation. 
Amalgamation  process  for  extraction  of  Silver  at  Freiberg. 
Treatment  of  Copper-matts  for  Silver.  Processes  employed 
to  supersede  the  amalgamation  of  Silver  Ores.  Augustin's 
process.  Patera's  process.  Ziervogel's  process.  Applica 
tions  of  Silver.  Standard  Silver.  Plated  articles.  Electro 
plating.  Silvering. 


x  Contents. 

PAGES 

GOLD  .        .        ...-        •        •    -    •        •        •          239'61 

Occurrence  of  Gold  in  Nature.  Alluvial  Gold.  Gold-quartz. 
Gold-washing.  Extraction  of  Gold  by  amalgamation. 
Parting  by  Sulphuric  Acid.  Parting  by  Nitric  Acid.  Re 
fining  of  Gold.  Extraction  of  Gold  from  Gold-quartz  in  the 
wet  way.  Testing  of  Gold.  Assay  of  Gold.  Manufacture 
of  Gold-leaf.  Gold -beating.  Gilding. 


MERCURY  ...... 

Ores  of  Mercury.  Extraction  of  Mercury  at  Almaden  ;  at 
Idria  ;  in  the  Palatinate.  Extraction  of  Mercury  from  Grey 
Copper  Ore.  Uses  of  Mercury.  Silvering  Looking-glasses. 
Magnetic  Amalgam. 


PLATINUM          .....        '•         v  276-84 

Treatment  of  Platinum  Ore  by  the  wet  and  dry  processes. 
Fusion  of  Platinum  with  the  Oxy-hydrogen  Blowpipe.  Uses 
of  Platinum.  Separation  of  Gold  and  Platinum  in  Assay  • 
ing. 

PALLADIUM  ........      284 


ANTIMONY 

Crude  Antimony.     Regulus  of  Antimony 


BISMUTH 

Extraction  of  Bismuth  at  Schneeberg  and  Joachimsthal. 
Newton's  fusible  alloy. 


Contents.  xi 

PAGES 

ALUMINUM 291-93 

Extraction  of  Aluminum  from  Bauxile. 


MAGNESIUM 294-95 

Extraction  of  Magnesium  from  Carnallite.     Extraction  of 
Sodium  from  Carbonate  of  Soda. 


CADMIUM 296 

Treatment  of  Zinc  Ores  for  extraction  of  Cadmium. 


ADDENDUM  TO  PAGE   251. 

Australian  gold  is  frequently  brittle  from  the  presence  of 
lead  or  antimony.  It  is  sometimes  refined  by  stirring  a  little 
corrosive  sublimate  (chloride  of  mercury)  into  the  melted 
gold,  when  the  chlorine  combines  with  the  base  metals, 
forming  chlorides  which  are  expelled  in  the  form  of  vapour, 
together  with  the  liberated  mercury.  F.  B.  Miller  has  intro 
duced  an  improved  process  for  refining  such  gold  by  forcing 
into  the  melted  metal  a  current  of  chlorine  gas,  through  the 
stem  of  a  tobacco-pipe.  The  chlorine  converts  the  silver 
present  in  the  gold  into  chloride  of  silver,  which  collects, 
in  a  melted  state,  upon  the  surface  of  the  gold,  whilst  any 
arsenic,  antimony,  bismuth,  lead,  or  zinc,  is  also  converted 
into  chloride,  and  driven  off  in  the  form  of  vapour.  The 
silver  is  afterwards  easily  extracted  from  its  chloride. 


METALS: 

THEIR    PROPERTIES    AND    TREATMENT. 

THE   METALS. 

THE  word  METAL  appears  to  be  derived  from  the  Greek 
per  ciXXa,  in  quest  of  other  things,  whence  come  /i£7-aXXaw, 
to  search  after,  to  explore,  or,  in  gold-diggers'  language,  to 
prospect,  and  the  corresponding  substantive  /le'raXXor,  a  mine. 

About  fifty  of  the  undecomposed  or  elementary  substances 
are  classed  together  under  the  head  of  METALS  by  the  chemist, 
because  they  manifest  certain  properties  when  acted  upon 
by  chemical  tesls,  without  regard  to  those  external  characters 
which  are  commonly  associated  with  the  idea  of  a  metal. 

Many  of  these  are  unfit  to  be  employed  in  the  metallic 
state  for  any  of  the  ordinary  uses  of  metals,  because  they 
cannot  be  exposed  to  the  action  of  air,  even  for  a  short 
time,  without  being  rusted  or  corroded,  by  combining  with 
the  oxygen  of  the  air,  to  such  an  extent  that  they  entirely 
lose  their  metallic  characters. 

Among  those  which  offer  sufficient  resistance  to  the  action 
of  air,  many  are  excluded  from  useful  application  in  their 
metallic  state,  on  account  of  their  rarity,  or  of  the  great  dif 
ficulty  which  is  experienced  in  extracting  them  from  their  ores. 

The  metals  which  are  employed  for  useful  purposes  in 
their  pure  or  metallic  state  are — 

Aluminum  Copper  Magnesium  Platinum 

Antimony  Gold  Mercury  Silver 

Bismuth  Iron  Nickel  Tin 

Cadmium  Lead  Palladium  Zinc 


2  Metals :  their  Properties  and  Treatment. 

On  considering  this  list,  it  will  be  seen  that  several  of  the 
metals  named  in  it  are  employed  to  produce  some  effect 
dependent  upon  a  peculiar  property  of  the  metal,  and  not 
upon  qualities  which  belong  to  it  in  common  with  the  rest. 
Thus,  mercury  or  quicksilver  is  used  for  amalgamating  or 
dissolving  other  metals,  and  also  as  a  suitable  liquid  for 
constructing  barometers  and  thermometers ;  antimony  owes 
its  usefulness  to  its  property  of  hardening  lead  and  tin  when 
melted  with  them;  bismuth  and  cadmium  are  employed  to 
render  lead  and  tin  capable  of  being  melted  at  lower  tem 
peratures  ;  nickel  is  used  to  whiten  copper  in  order  to  make 
German  silver;  and  magnesium  is  valuable  for  its  property 
of  burning  easily  with  production  of  a  brilliant  white  light. 

Moreover,  gold,  platinum,  palladium,  and  silver,  being 
comparatively  rare,  and  aluminum  being  obtainable  by  a 
somewhat  costly  process,  the  useful  applications  of  these 
metals  are  limited  by  their  high  price,  so  that  there  remain 
only  TIN,  LEAD,  COPPER,  IRON  and  ZINC  to  be  considered 
as  metals  largely  employed  for  useful  purposes. 

The  qualities  possessed  by  these  metals,  rendering  them 
fit  for  purposes  which  could  not  be  fulfilled  by  non-metallic 
substances,  are  lustre,  or  the  power  of  reflecting  light; 
tenacity,  or  resistance  to  any  attempt  to  pull  asunder  their 
particles ;  malleability,  or  the  capability  of  being  hammered 
or  rolled  into  thin  sheets ;  ductility,  or  the  property  of  being 
drawn  out  into  wire ;  high  specific  gravity,  or  relative  weight ; 
high  conducting  power,  for  heat  and  electricity;  and  fusibility, 
or  the  property  of  becoming  liquid  when  heated. 

METALLIC  LUSTRE. — The  power  of  reflecting  the  rays  of 
light  is  possessed  in  a  much  higher  degree  by  metals  than 
by  non-metallic  substances.  Although  some  examples  of 
the  latter  class,  such  as  iodine  and  plumbago,  reflect  much 
of  the  light  which  falls  upon  smooth  surfaces  of  them,  they 
have  a  black  appearance,  caused  by  their  absorbing  a  large 
proportion  of  the  luminous  rays,  which  is  quite  different 
from  the  true  metallic  lustre.  Iron,  in  the  form  of  steel,  is 


Metallic  Lustre. —  Tenacity.  3 

capable  of  exhibiting  this  lustre  in  very  great  perfection, 
because  the  hardness  of  steel  allows  its  surface  to  be  ground 
perfectly  smooth  by  the  application  of  fine  particles  of  very 
hard  substances,  such  as  emery  and  diamond-dust,  which 
rub  off  minute  projections  from  the  surface  without  pro 
ducing  scratches  or  indentations.  A  surface  so  polished 
sends  back  directly  to  the  eye  of  the  observer  almost  all  the 
light  falling  upon  it,  whilst  a  rough  surface,  being  made  up 
of  a  number  of  small  surfaces,  scatters  the  reflected  rays  in 
all  directions.  Tin  is  naturally  a  brilliant  metal,  but  is  not 
hard  enough  to  be  polished,  like  steel;  if,  however,  it  be 
dissolved  in  twice  its  weight  of  melted  copper,  an  alloy  of 
great  hardness  and  brilliancy  is  formed,  which  is  employed 
for  the  specula  or  mirrors  of  reflecting  telescopes.  Zinc  and 
lead  exhibit  the  metallic  lustre  in  an  inferior  degree,  and 
become  dull  when  exposed  to  air,  because  the  metal  at  the 
surface  combines  with  oxygen,  forming  a  thin  film  of  oxide 
which  has  no  metallic  lustre.  The  natural  lustre  of  silver  is 
very  great,  and,  if  it  be  hardened  by  admixture  with  a  little 
copper,  it  becomes  susceptible  of  a  very  high  polish  which  is 
not  dimmed  by  the  action  of  the  oxygen  of  air,  though  it  is 
easily  tarnished  by  sulphur  existing  in  foul  air  in  the  form  of 
sulphuretted  hydrogen.  The  splendid  combination  of  lustre 
and  colour  exhibited  by  burnished  gold  is  proverbial,  and  is 
undiminished  by  the  action  of  the  atmosphere.  The  lustre 
of  palladium  and  platinum  resembles  that  of  silver,  and  is 
not  affected  by  oxygen  or  sulphur  in  the  air.  Aluminum 
has  also  a  permanent  lustre,  though  inferior  to  that  of  silver. 
When  dissolved  in  nine  times  its  weight  of  melted  copper, 
aluminum  forms  a  hard  yellow  alloy  capable  of  being  polished 
to  resemble  gold,  but  becoming  slowly  tarnished  by  the 
action  of  the  oxygen  in  air. 

TENACITY. — The  strength  with  which  the  metals  oppose 
any  attempt  to  pull  asunder  their  particles  is  one  of  their 
most  useful  properties,  and  is  determined  by  ascertaining 
the  exact  weight  which  must  be  suspended  from  the  ends  of 


4          Metals :  their  Properties  and  Treatment. 

wires  or  rods  of  equal  diameter,  in  order  to  break  them. 
The  weight  required  to  break  a  given  metallic  wire  is  found 
to  vary  according  to  the  manner  in  which  the  strain  is 
applied,  the  resistance  of  the  wire  being  greater  when  the 
whole  of  the  breaking  weight  is  applied  at  once  than  when 
it  is  added  gradually,  probably  because,  in  the  latter  case, 
the  wire  becomes  stretched  and  weakened  by  each  additional 
weight. 

Steel  (iron  combined  with  about  -g^th  part  of  carbon)  is 
by  far  the  most  tenacious  of  metals,  and  lead  is  the  least 
tenacious  of  those  in  ordinary  use. 

If  the  weight  required  to  pull  asunder  a  wire  of  lead  be 
taken  as  unity,  that  required  by  similar  wires  of  the  other 
metals  will  found  to  approach  nearly  to>  the  numbers  con 
tained  in  the  following  table  : — 


Lead 

Tin 

Zinc 

Palladium 

Gold 


Relative  Tenacity  of  the  Metals. 

Silver     . 
Platinum 
Copper  . 
Iron 
Steel       . 


42 


The  tenacity  of  metals  is  very  seriously  affected  by  varia 
tions  in  their  structure,  purity  and  temperature.  Thus,  rods 
of  metal  which  have  been  cast  in  a  mould  are  generally 
weaker  than  rods  of  equal  dimensions  made  by  drawing  the 
metal  through  the  gradually  diminishing  holes  of  the  wire- 
drawer's  plate.  The  tenacity  of  iron  rods  which  have  been 
rolled  until  they  have  acquired  a  fibrous  structure,  is 
much  higher  than  that  of  rods  which  are  crystalline  in  tex 
ture,  the  metal  tending  to  break  asunder  where  the  smooth 
surfaces  of  the  separate  crystals  are  in  contact  with  each 
other. 

The  tenacity  of  a  metal  when  hot  is,  as  might  be  anti 
cipated,  less  than  its  tenacity  when  cold ;  and  if  the  metal 
be  made  red-hot  and  allowed  to  cool  slowly,  it  will  generally 
be  found  to  have  diminished  in  tenacity,  probably  because 


Malleability.  5 

a  high  temperature  tends  to  encourage  the  formation  of  a 
crystalline  structure.  The  effect  of  the  presence  of  im 
purities  upon  the  tenacity  of  metals  will  be  more  appro 
priately  studied  when  the  individual  metals  are  under  con 
sideration,  but  it  may  be  stated  generally  that  chemical 
purity  is  not  of  necessity  accompanied  by  the  highest  degree 
of  tenacity.  Thus,  the  small  proportion  of  carbon  present 
in  steel  is  seen  in  the  above  table  to  have  greatly  increased 
the  tenacity  of  the  iron,  and  pure  zinc  has  a  much  lower 
tenacity  than  the  ordinary  zinc  of  commerce. 

MALLEABILITY. — The  facility  with  which  a  mass  of  metal 
can  be  hammered  or  rolled  into  a  thin  sheet  without  being 
torn,  must  depend  partly  upon  its  softness,  and  partly  upon 
its  tenacity.  If  it  depended  upon  softness  alone,  lead  should 
be  the  most  malleable  of  ordinary  metals ;  but,  although  it  is 
easy  to  hammer  a  mass  of  lead  into  a  flat  plate,  or  to  squeeze 
it  between  rollers,  any  attempt  to  reduce  it  to  an  extremely 
thin  sheet  fails  from  its  want  of  tenacity,  which  causes  it  to 
be  worn  into  holes  by  percussion  or  friction.  On  the  other 
hand,  if  malleability  were  entirely  regulated  by  tenacity,  iron 
would  occupy  the  first  place,  whereas,  on  account  of  its 
hardness,  it  is  the  least  malleable  of  metals  in  ordinary  use  j 
whilst  gold,  occupying  an  intermediate  position  with  respect 
to  tenacity,  is  the  most  malleable,  which  appears  surprising 
to  those  who  are  only  acquainted  with  gold  in  its  ordinary 
forms  of  coin  and  ornament,  in  which  it  is  hardened  and 
rendered  much  less  malleable  by  the  presence  of  copper  and 
silver. 

During  the  rolling  or  lamination  of  metals  their  particles 
are  obviously  squeezed  into  unnatural  positions ;  it  becomes 
necessary,  therefore,  in  order  to  avoid  breaking,  to  enable 
the  particles  to  resume  their  former  relative  situations  •  this 
is  effected  by  heating  the  metallic  sheet  after  every  two  or 
three  rollings,  and  allowing  it  to  cool  slowly,  a  process  of 
annealing  similar  to  that  by  which  glass  vessels  are  rendered 
less  brittle. 


6          Metals :  their  Properties  and  Treatment. 

.    In  the  following  table  the  ordinary  metals  are  arranged  in 
the  order  of  malleability  : — 

Table  of  Malleability. 

1.  Gold.  4.  Tin.  7.  Zinc. 

2.  Silver.  5.   Platinum.  -  8.   Iron. 

3.  Copper.  6.  Lead. 

DUCTILITY. — The  ease  with  which  a  metal  can  be  elon 
gated  into  a  wire,  by  being  drawn  through  the  gradually 
diminishing  holes  of  the  wire-drawer's  plate,  will  be  greater 
in  proportion  to  the  softness  of  the  metal ;  but  the  thinness 
of  the  wire  to  which  it  can  be  reduced  is  regulated  by  the 
tenacity  of  the  metal,  which  enables  it  to  resist,  without 
breaking,  the  force  required  to  draw  it  through  the  holes. 
And  it  is  found  that  their  tenacity  has  more  influence  upon 
the  ductility  of  metals  than  upon  their  malleability,  for  the 
particles  of  a  weak  metal,  like  tin,  may  cohere  under  the 
hammer,  although  they  would  be  easily  torn  apart  by  the 
direct  pull  necessary  in  wire-drawing. 

Gold,  silver,  and  platinum,  which  occupy  an  intermediate 
position  with  respect  to  tenacity,  are  the  most  ductile  of  the 
metals,  whilst  tin  and  lead,  which  are  lowest  in  tenacity,  are 
the  least  ductile,  though  their  softness  gives  them  a  higher 
place  in  the  order  of  malleability. 

Table  of  Ductility. 

1.  Gold.  5.  Copper.  8.  Zinc. 

2.  Silver.  6.  Palladium.  9.   Tin. 

3.  Platinum.  7.  Aluminum.  10.   Lead. 

4.  Iron. 

The  metals  require  annealing  during  the  process  of 
wire-drawing,  as  in  that  of  lamination,  and  for  a  similar 
reason. 

SPECIFIC  GRAVITY. — The  relative  weights  of  equal  bulks 
of  the  metals  exercise  considerable  influence  upon  their 
useful  applications.  The  relative  weight  of  gold  being  very 
high  it  is  well  adapted  for  a  circulating  medium,  a  large 


Specific  Gravity. 


value  being  compressed  into  a  portable  form.  On  the  other 
hand,  iron  would  be  employed  with  far  less  advantage  in 
building  if  its  relative  weight  did  not  happen  to  be  low, 
whilst  aluminum,  being  the  lightest  of  metals  in  ordinary 
use,  is  particularly  well  adapted  for  the  production  of  small 
weights,  as  fractions  of  a  grain,  which  shall  yet  be  large 
enough  to  handle  ;  such  weights  being  nearly  nine  times  as 
large  when  made  of  aluminum  as  they  are  when  platinum  is 
employed,  as  was  the  case  before  the  introduction  of  alu 
minum. 

The  specific  gravities,  or  comparative  weights  of  equal 
bulks  of  the  metals,  are  generally  expressed  by  numbers 
which  show  that  each  metal  is  so  many  times  as  heavy  as  an 
equal  bulk  of  pure  distilled  water  at  the  ordinary  tempera 
ture  (60°  F.)  ;  thus,  zinc  is  a  little  more  than  seven  times  as 
heavy  as  an  equal  bulk  of  water,  so  that  its  specific  gravity 
is  expressed  by  7  and  a  fraction. 

The  first  column  of  numbers  in  the  following  table  gives 
the  specific  gravities  of  the  metals  in  round  numbers,  which 
can  be  easily  retained  in  the  memory,  and  are  sufficiently 
exact  for  ordinary  purposes,  the  more  accurate  numbers 
usually  employed  in  scientific  works  being  given  in  the  next 
column  :  — 


Table  of  Specific  Gravities  of  the  Metals. 


Platinum 

2il 

21-53 

Nickel  . 

Gold     . 

19! 

19-34 

Iron 

Mercury 

I3| 

13-59 

Tin       . 

Palladium 

II- 

u-8 

Zinc      . 

Lead     . 

Il| 

11-36 

Antimony 

ilver  . 

-I0! 

Aluminum 

Bismuth 

9-79 

Magnesium 

Copper 

9" 

8-95 

7^ 


'i 


8-82 
7-84 
7-29 
7-14 
6-7i 
2-67 

1-74 


CONDUCTING  POWER  OF  METALS  FOR  HEAT.  —  The 
sensation  of  cold  when  the  hand  is  placed  upon  a  piece  of 
metal  of  the  ordinary  temperature  of  the  air  shows  us  that 
metals  are  better  conductors  of  heat  than  non-metallic 


Metals :  their  Properties  and  Treatment. 

bodies,  for  the  particles  of  metal  which  are  first  warmed  by 
contact  with  the  hand  give  up  the  acquired  heat  to  the 
neighbouring  particles,  and  being  thus  cooled  to  nearly  their 
former  temperature,  are  able  to  abstract  a  fresh  supply  of 
heat  from  the  hand ;  whereas,  when  the  hand  is  placed  upon 
wood,  or  other  inferior  conductors  'of  heat,  the  particles  in 
contact  with  it  are  warmed  by  the  removal  of  a  trifling 
amount  of  heat  from  the  hand,  and  are  not  soon  cooled 
again  by  parting  with  their  heat  to  the  particles  adjoining. 
In  consequence  of  the  rapidity  with  which  heat  applied  to 
one  portion  of  a  mass  of  metal  is  communicated  to  the 
whole  of  the  particles  composing  it,  metals  may  be  suddenly 
heated  or  cooled  with  much  less  risk  of  causing  them  to 
crack  or  fly  than  is  the  case  with  non-metallic  substances. 
When  an  earthenware  pipkin  or  a  glass  bottle  is  placed  upon 
the  fire,  the  outside  immediately  becomes  much  hotter  than 
the  inside,  and  being  expanded  by  the  heat,  tears  apart  the 
particles  of  the  inside  of  the  vessel  and  produces  a  crack, 
but  in  the  case  of  a  metallic  vessel  the  heat  is  rapidly  trans 
mitted,  and  all  parts  of  the  vessel  are  expanded  almost 
simultaneously.  The  much  greater  rapidity  with  which 
water  can  be  heated  in  metallic  vessels  is  another  useful 
result  of  the  superior  conducting  power  of  the  metals. 

In  the  following  table  the  metals  are  arranged  in  the 
order  of  their  conducting  power,  the  first  being  the  best 
conductor  : — 

Table  of  Conducting  Power  for  Heat. 

1.  Silver.  5.  Zinc.  9.  Lead. 

2.  Gold.  6.  Iron.  lo.  Antimony. 

3.  Copper.  7.  Tin.  II.  Bismuth. 

4.  Aluminum.  8.  Platinum. 

CONDUCTING  POWER  OF  METALS  FOR  ELECTRICITY. — 
The  conducting  power  for  electricity,  of  metals,  refers  to  the 
facility  with  which  an  electric  disturbance  excited  in  one 
portion  of  a  mass  of  metal  is  transmitted  to  the  other  par 
ticles  composing  the  mass.  Thus,  a  very  slight  electric  dis- 


Fusibility. 


turbance  at  one  end  of  a  copper  wire  is  sufficient  to  produce 
movement  in  a  telegraph  needle  at  the  other  extremity, 
whilst  a  much  greater  amount  of  disturbance,  or,  in  other 
words,  a  more  powerful  current,  is  required  if  an  iron  wire 
of  the  same  length  and  thickness  be  employed. 

Only  one  non-metallic  substance — carbon,  in  some  of  its 
varieties — at  all  approaches  to  the  metals  in  the  power  of 
conducting  electricity. 

Those  metals  which  are  the  best  conductors  of  heat  are 
also  the  best  conductors  of  electricity,  and  in  both  cases  the 
conducting  power  is  seriously  impaired  by  the  presence  in 
the  metal  even  of  small  quantities  of  other  metals,  or  of 
non-metallic  bodies,  as  well  as  by  an  increase  of  temperature 
in  the  metal.  When  heated  to  the  boiling  point  of  water, 
the  metals  have  only  about  three-fourths  of  the  conducting 
power  which  they  exhibit  at  the  freezing  point. 

The  following  table  shows  the  relative  conducting  power 
of  the  most  important  metals,  in  a  pure  state,  at  32°  R,  the 
conducting  power  of  silver,  which  is  higher  than  that  of  any 
other  metal,  being  taken  as  1000  : — 

Table  of  Conducting  Power  for  Electricity. 
Silver  =   1000 


Copper  . 

Gold      ; 

Zinc 

Palladium 

Platinum 

Iron 


999 
779 
290 
184 
1 80 
1 68 


Nickel    . 
Tin 

Lead      . 
Antimony 
Bismuth 


123 

83 
46 

12 


FUSIBILITY. — Although  the  property  of  becoming  liquid 
at  high  temperatures  is  not  confined  to  the  metals,  it  must 
be  mentioned  among  the  properties  which  conduce  to  their 
utility,  for  it  enables  the  founder  to  produce  a  large  number 
of  objects  of  a  given  pattern  with  little  expenditure  of  time 
and  labour,  and  offers  to  the  worker  in  metals  a  ready 
method  of  soldering  together,  in  a  durable  manner,  the  sepa- 


io        Metals:  their  Properties  and  Treatment. 

rate  pieces  of  his  work.  Tin  and  lead,  being  the  most 
fusible  of  ordinary  metals,  are  the  constituents  of  ordinary 
solder,  whilst  iron  (wrought  iron),  as  the  least  fusible  of  the 
common  metals,  is  used  for  firebars,  melting-pots,  and  simi 
lar  purposes. 

Table  of  Fusibility. 

Tin  melts  at  442°  F.     Silver  melts  at  1800°  F. 

Cadmium  442  Copper  ,  1990 


Bismuth 
Lead 
Zinc 
Antimony* 


507  Gold 

617  Cast  Iron 

773  Steel 

1150  Wrought  Iron 


2000 

2780 

4000 

above  4000 


Platinum  melts  only  in  the  oxy-hydrogen  blowpipe  flame. 

In  practical  work  the  temperature  is  commonly  inferred 
from  the  appearance  of  the  fire  ;  thus,  the  red  heat  of  an 
ordinary  domestic  fire  is  roughly  valued  at  1000°  F.,  so  that 
tin,  lead,  and  zinc  can  be  very  easily  melted  in  a  crucible  or 
ladle  placed  in  such  a  fire;  but  aluminum,  silver,  copper, 
and  gold,  require  a  bright  red  (cherry  red)  or  furnace  heat  to 
melt  them ;  cast  iron  requires  a  very  bright  red  heat,  only 
attainable  in  a  furnace  with  a  very  good  draught ;  and  for 
melting  steel,  a  furnace  of  special  construction  (wind  fur 
nace]  is  employed.  Wrought  iron  can  be  fused  only  at  a 
white  heat,  producible  by  a  blast  of  air  in  a  forge,  and  plati 
num  melts  at  a  greenish  white  heat  in  the  flame  of  hydrogen 
supplied  with  pure  oxygen.  The  production  of  a  tempera 
ture  adequate  to  the  fusion  of  steel  and  wrought  iron  in 
large  quantities  has  been  much  facilitated  by  the  introduc 
tion  of  Siemens'  regenerative  furnace,  in  which  the  waste 
heat  of  the  fire,  instead  of  escaping  up  the  chimney  into  the 
air,  is  accumulated  in  masses  of  fire-brick,  and  restored 
again  to  the  furnace. 

*  Estimates  of  temperature  above  the  fusing  point  of  zinc  cannot  be 
regarded  as  exact,  on  account  of  the  difficulty  of  ascertaining  them. 


Properties  of  Iron.  1 1 


IRON. 

With  respect  to  its  useful  properties,  iron  occupies  the 
first  place  among  the  metals.  By  far  the  strongest,  and,  at 
the  same  time,  one  of  the  lightest,  its  applications  in  the 
arts  of  construction  are  much  more  numerous  than  those  of 
any  other  metal.  Being  capable  of  assuming,  according  to 
the  treatment  which  it  undergoes,  the  forms  of  wrought  iron, 
cast  iron,  and  steel,  it  is  susceptible  of  the  widest  variations 
in  its  characters.  Extracted  from  its  ores  in  the  form  of 
cast  iron,  it  is  melted  with  comparative  facility,  and,  accord 
ing  to  the  mode  of  operating  in  the  foundry,  may  be  made 
to  yield  castings  which  are  easily  filed  and  turned,  or  may 
be  rendered  so  hard  that  no  tool  is  able  to  touch  it.  By 
judicious  treatment  with  heat  and  atmospheric  air  the  cast 
iron  is  converted  into  steel,  the  strongest,  and  one  of  the 
hardest  and  most  elastic  of  all  materials,  as  well  as  the  only 
one  of  which  a  magnetic  needle  can  be  made.  Continued  a 
little  further,  the  joint  action  of  heat  and  atmospheric  air 
converts  the  steel  into  wrought  iron,  possessing  great  strength 
and  toughness,  yet  soft  enough  to  be  turned,  bored,  and 
punched  with  ease,  and,  especially  when  heated,  to  be  rolled 
and  twisted  into  the  most  varied  forms  without  cracking. 
With  less  disposition  to  melt  under  the  action  of  heat 
than  any  other  common  metal,  wrought  iron  is  sufficiently 
softened  at  a  bright  red  heat  to  be  welded  or  joined  to 
another  piece  in  the  most  perfect  manner,  without  the  use 
of  solder  of  any  kind.  Being  capable  of  acquiring  and  of 
losing  the  properties  of  a  magnet  with  great  rapidity,  soft 
iron  (wrought  iron)  is  the  only  material  which  is  adapted  for 
the  construction  of  electro-magnetic  and  magneto-electric 
apparatus. 


1 2        Metals :  their  Properties  and  Treatment. 

It  is  not  too  much  to  assert  that  scarcely  a  step  of  im 
portance  has  ever  been  made  in  the  industrial  progress  of 
any  community  to  which  some  one  of  the  three  modifica 
tions  of  iron  has  not  been  indispensable. 

Possessed  of  so  many  valuable  qualities,  iron  is  still  the 
cheapest  of  all  the  metals,  since  the  ores  from  which  it  is 
extracted  are  scattered  in  profusion  through  the  crust  of  the 
earth,  and  can  be  made  to  yield  the  metal  in  abundance  by 
a  moderate  expenditure  of  time,  labour,  and  fuel. 

ORES  OF  IRON. — Iron  in  the  metallic  condition,  or  native 
iron,  is  very  rarely  found  in  nature.  Nearly  all  the  speci 
mens  which  have  been  examined  have  been  meteoric  iron, 
occurring  in  masses  of  irregular  form,  which  have  descended 
upon  the  surface  of  the  earth,  but  whence  is  at  present  only 
a  matter  for  speculation.  Such  masses  have  been  found 
containing  93  parts  in  the  hundred,  of  metallic  iron,  always 
associated  with  nickel,  and  sometimes  with  small  quanti 
ties  of  other  metals.  They  occur  of  such  size  as  to  weigh 
1 6  cwt.  or  17  cwt.  A  small  one,  which  was  found  at  Lenarto 
in  Hungary  and  weighed  about  ipolbs.,  was  remarkably 
malleable,  and  its  analysis  furnished  the  following  re 
sults  :— 

Lenarto  Meteoric  Iron. 
Specific  Gravity,  7-79 

Iron  .  .  .  90-883 

Nickel  .  .  .  8-450 

Cobalt  .  .  .  0-665 

Copper  .  .  ;  0-002 

100-000 


A  recent  examination  of  this  meteoric  iron  has  led  to  the 
very  interesting  discovery  that  it  contains  about  twice  and  a 
half  its  volume  of  hydrogen  gas,  apparently  in  an  uncom- 
bined  state. 

Iron  is  most  commonly  found  in  a  state  of  chemical  com 
bination  with  oxygen  or  sulphur,  which  disguise  its  metallic 


Ores  of  Iron.  13 

properties  and  convert  it  into  earthy  or  stony  masses.  The 
compound  of  iron  with  oxygen,  or  oxide  of  iron,  which  is 
familiar  to  us  in  the  form  of  rust,  occurs  in  a  very  large 
number  of  mineral  substances,  and  is  often  the  cause  of  their 
colour.  Sand,  clay,  and  gravel,  commonly  owe  their  yellow, 
brown,  or  red  shade  to  the  presence  of  oxide  of  iron,  a 
small  proportion  of  which  imparts  a  very  distinct  colour. 
No  mineral  substance,  however,  would  be  considered  as  an 
ore  of  iron  which  contained  less  than  about  twenty  parts  of 
iron  in  the  hundred,  for  otherwise  it  would  not  repay  the 
cost  of  its  extraction. 

The  following  table   includes    the    mineral    substances 
which  are  commonly  regarded  as  ores  of  iron  : — 


Ores  of  Iron. 

Composition 

Iron  in  100  ports 
of  pure  Ore 

Magnetic  Iron  Ore  . 

Iron,  Oxygen 

72 

Red  Haematite 

Iron,  Oxygen 

70 

Specular  Ore  . 

Iron,  Oxygen 

70 

Brown  Haematite     . 

/Iron,  Oxygen,    "1 

\     1*7       .                                                      > 

60 

X  Water                 / 

Spathic  Iron  Ore     . 

/Iron,  Oxygen,    "1 
L  Carbonic  Acid  / 

48 

Clay  Iron  Stone 

f  Iron,  Oxygen,    1 
<  Carbonic  Acid,   S 

Variable, 

I  Clay                    J 

17  to  50 

(  Iron,  Oxygen,    ~| 

Black-band  Ore 

J  CarbonicAcid,    1 
]  Clay,  Bitumin-    [ 

Variable, 
21  to  43 

|_     ous  matter      J 

Iron  Pyrites*  .     '  . 

Iron,  Sulphur 

46 

Magnetic  Iron  Ore,  or  Magnetite,  derives  its  name  from 
Magnesia  in  Asia  Minor,  where  its  power  of  attracting  iron 
and  steel  was  first  observed.  One  variety  of  the  ore  con 
stitutes  the  loadstone^  which  confers  magnetic  properties  upon 

Iron  Pyrites  is  not  worked  as  an  ore  of  iron,  on  account  of  the 
great  difficulty  of  separating  all  the  sulphur  from  the  metal. 

t  Probably  corrupted  from  lead-stone,  the  stone  which  leads  or  guides, 
in  allusion  to  its  use  for  making  the  needle  of  the  mariner's  compass 


14        Metals :  their  Properties  and  Treatment. 

steel.  This  variety  occurs  chiefly  in  Siberia  and  the  Hartz. 
Some  of  the  common  varieties  of  the  ore  do  not  attract  iron, 
although  they  are  capable,  like  steel,  of  becoming  magnetic 
when  brought  into  contact  with  powerful  magnets. 

This  ore  is  generally  met  with  in  compact  heavy  masses 
of  an  iron  black  or  grey  colour,  and  with  considerable 
lustre.  Its  specific  gravity  varies  from  4-9  to  5-2.  It 
abounds  chiefly  in  the  northern  parts  of  the  globe,  and  is 
found  in  immense  masses  in  Norway,  Sweden,  Russia,  and 
North  America,  being  the  most  important  iron  ore  in  those 
countries.  The  iron  extracted  from  it  is  generally  of  ex 
cellent  quality,  though  it  is  occasionally  deteriorated  by 
sulphur  and  phosphorus,  which  are  derived  respectively 
from  iron  pyrites  and  from  apatite  (phosphate  of  lime), 
which  are  sometimes  found  associated  with  the  magnetic  ore. 
The  bulk  of  the  Swedish  iron,  so  much  valued  for  the 
manufacture  of  steel,  is  extracted  from  the  magnetic  ore  at 
Dannemora,  where  it  is  worked  in  an  open  quarry. 

Magnetic  iron  ore  often  contains  titanic  acid,  the  oxide  of 
the  metal  titanium,  and  this  is  especially  the  case  with  a 
variety  of  the  ore  which  occurs  as  a  heavy  black  shining 
sand  in  India,  Nova  Scotia,  and  New  Zealand. 

Red  Htzmatite  has  been  so  called  from  the  Greek  word 
signifying  blood,  on  account  of  its  dark  red  colour,*  and  is 
sometimes  erroneously  called  bloodstone  (the  true  bloodstone 
being  a  dark  green  variety  of  silica  (heliotrope)  with  red 
spots).  In  appearance  it  is  the  most  striking  of  the  ores  of 
iron,  sometimes  appearing  in  rounded  masses  having  exter 
nally  a  liver  colour  with  considerable  lustre,  and  internally 
made  up  of  layers  having  the  appearance  of  the  thick  shell 
of  some  huge  fruit,  or  of  bundles  of  fibres,  which  look 
like  petrified  wood.  The  specific  gravity  of  this  variety  is 

magnetic.  In  a  similar  way  we  have  load-star,  the  star  which  leads 
towards  the  pole ;  leadsman,  one  who  guides — a  pilot ;  load  or  lode, 
the  leading  vein  in  a  mine. 

*  The  termination  ite,  so  generally  found  in  the  names  of  minerals, 
was  originally  derived  from  the  Greek  word  for  stone. 


Ores  of  Iron.  1 5 

about  5*0.  Such  specimens  are  in  general  remarkably  hard, 
and  are  useful  for  burnishing  metals.  But  it  is  occasionally 
found  in  much  softer  earthy-looking  masses  of  a  brighter 
colour,  and  not  uncommonly  associated  with  clay. 

Red  haematite  is  much  more  generally  diffused  than 
magnetite,  and  is  found  abundantly  in  this  country,  at 
Whitehaven  (Cumberland)  and  Ulverstone  (Lancashire),  as 
well  as  in  Glamorganshire.  The  compact  variety  is  exceed 
ingly  pure,  and  furnishes  iron  of  the  very  best  quality,  but 
its  very  dense  structure  renders  it  difficult  to  smelt  alone  in 
English  furnaces,  so  that  it  is  customary  to  mix  it  with  some 
lighter  ores  of  inferior  purity,  a  practice  which  detracts  from 
the  excellence  of  the  iron  obtained. 

This  ore  is  also  abundant  in  Ireland  (Balcarry  Bay), 
North  America,  Saxony,  Bohemia,  and  the  Hartz. 

Specular  Iron  Ore  is  identical  in  composition  with  red 
haematite,  though  its  appearance  is  so  different,  for  it  forms 
crystalline  masses,  and  sometimes  separate  crystals  of  a 
steel-grey  colour  and  brilliant  lustre,  whence  it  derives  its 
name  (speculum  [Latin],  a  mirror).  It  is  also  called  Iron- 
glance  (  Glanz  [German],  lustre),  and  in  one  of  its  varieties, 
made  up  of  shining  scales,  Micaceous  Iron  Ore  (micare 
[Latin],  to  shine).  When  scratched  with  a  knife,  or  re 
duced  to  powder,  it  exhibits  the  red  colour  of  haematite.  The 
specific  gravity  of  specular  iron  ore  is  5-2.  The  island  of 
Elba  has  long  been  noted  for  its  specular  iron  ore,  and  it  is 
also  found  in  considerable  quantity  in  Russia  and  Spain. 
The  excellent  iron  of  Nova  Scotia  is  extracted  from  the 
specular  ore  of  the  Acadian  mines. 

Brown  Hcematite  contains  the  same  oxide  of  iron  as  red 
haematite,  but  in  a  state  of  chemical  combination  with  water, 
the  latter  varying  from  ten  to  fourteen  parts  in  a  hundred 
parts  of  the  ore.  Its  appearance  varies  widely  in  different 
specimens.  Some  form  globular  masses  of  considerable 
size,  others  occur  in  small  round  grains  (pea  iron  ore] ; 
occasionally  it  occurs  in  stalactites ;  the  various  soft  earthy 


1 6         Metals :  their  Properties  and  Treatment. 

ochres*  and  umbers-^  consist,  for  the  most  part,  of  brown 
haematite,  the  dark  brown  shade,  in  the  latter  case,  being 
caused  by  the  presence  of  an  oxide  of  manganese. 

In  this  country  brown  haematite  is  found  at  Alston  Moor 
(Cumberland)  and  in  Durham,  but  it  is  a  much  more  im 
portant  iron  ore  in  France.  Some  varieties  of  it  contain  a 
considerable  proportion  of  phosphorus  (in  the  form  of  phos 
phoric  acid  combined  with  oxide  of  iron),  which  materially 
affects  the  quality  of  the  iron  extracted  from  them. 

The  Black  Britsh  Ore  of  the  Forest  of  Dean  is  a  brown 
haematite  containing  89  parts  of  peroxide  of  iron,  and  10 
parts  of  water,  and  yields  most  of  the  iron  used  for  making 
tin-plate. 

The  Lake  Ores  of  Sweden  consist  of  a  variety  of  brown 
haematite  ore  which  occurs  at  the  bottom  of  lakes,  and  is 
collected  by  dredging  with  a  kind  of  iron  sieve  attached  to 
a  long  pole,  and  thrust  down  through  a  hole  in  the  ice,  the 
mud  being  washed  away  from  the  ore  by  shaking  the  sieve 
up  and  down  under  water.  In  this  way  a  man  will  some 
times  collect  as  much  as  a  ton  of  ore  in  a  day. 

Spathic  Iron  Ore  (Spath  [German],  spar),  or  sparry  iron 
ore,  is  composed  of  carbonate  of  iron,  or  iron  combined  with 
oxygen  and  carbonic  acid.  Some  specimens  consist  of  a 
collection  of  nearly  transparent  shining  crystals,  which  are 
almost  colourless,  and  have  the  same  crystalline  form  as  cal 
careous  spar  (carbonate  of  lime).  It  is  found  in  extensive 
beds  in  Styria  and  Carinthia.  Spathic  ore  almost  invariably 
contains  manganese,  which  especially  adapts  it  for  the  ma 
nufacture  of  certain  kinds  of  steel,  whence  it  has  sometimes 
been  termed  steel  ore.  This  ore  is  also  found  at  Wearsdale 
in  Durham,  and  on  the  Brendon  Hills  in  Somersetshire. 

Clay  Iron  Stone  or  Argillaceous  J  Iron  Ore  contains  the 

*  Derived  from  the  Greek  for  sallow,  in  allusion  to  their  yellow 
colour. 

t  From  umbra  (Latin),  shade,  on  account  of  their  darker  tint. 
£  Argilla  (Latin),  clay. 


Ironstones  of  the  Coal  Measures.  !  7 

iron  in  the  same  form  of  chemical  combination  (carbonate 
of  iron),  in  which  it  exists  in  spathic  iron  ore,  but  in  a  state 
of  intimate  mixture  with  clay.     This  ore  is  by  far  the  most 
important  of  British  iron  ores,  being  that  which  is  most  ex 
tensively  worked  in  this  country.     It  occurs  in  great  abun 
dance  around  Dudley,  in  Staffordshire,  in  Yorkshire,  Derby 
shire,  and  in  South  Wales.     Both  this  ore  and  the  black 
band  ore  are  found  in  layers  which  occur  alternately  with 
beds  of  coal,  limestone,  clay,  and  shale,  whence  they  are 
ften  spoken  of  as  the  Ironstones  of  the  Coal  Measures,  and 
the  circumstance  that  the  same  pit,  or  neighbouring  pits, 
will  furnish  the  coal  employed  for  smelting  the  ore  the  lime 
stone  used  as  a  flux,  and  even  the  clay  for  making  fire 
bricks  for  the  furnace,  allows  English  iron  to  be  produced 
it  a  price. with  which,  until  lately,  other  countries  found 
t  impossible   to   compete.     The   coal  formations   of  Bel 
gium  and  Silesia  also  furnish  large  supplies  of  clay  iron- 

This  ore  is  found  sometimes  in  continuous  beds      nd 

sometimes  in  irregular  globular  masses,  imbedded  in  clay  • 

3   moderately   hard   and   stony,  and   varies   in   colour' 

through  different  shades  of  grey,  slaty-blue,  and  brown      It 

is  lighter  than  the  preceding  ores,  and  a  cursory  observer 

might  regard  it  as  a  stone  rather  than  a  metallic  ore      The 

proportions  of  carbonate  of  iron  and  clay  contained  in  the 

ore  vary  considerably,  the  former  amounting  to  80  or  go 

s  m  the  hundred  in  some  specimens,  and  in  others  not 

exceeding  half  the  weight  of  the  ore. 

Blackband  Ore  differs  from  clay  iron-stone  only  by  con- 

ung,  in  addition  to  its  other  constituents,  a  quantity  of 

bituminous  or  coaly  matter,  sometimes  amounting  to  one- 

wMch  it  d"61"     °f  Ae  °re'  and  impardng  the  Colour  *>* 
which  i    derives  its  name.     Lanarkshire  and  Ayrshire,  in 

Scotland,  contain  extensive  deposits  of  blackband  iron  ire 
first  brought  to  light  in  iSor.  The  presence  of  so  much 
combustible  matter  allows  the  ore  to  be  smelted  witness 


1 8         Metals :  their  Properties  and  Treatment. 

expenditure   of  fuel.     Blackband   ores  are  also  mined   in 
Prussia. 

The  Northamptonshire  iron  ore,  which  is  found  in  the 
oolite  limestone  in  that  county,  appears  to  have  been  formed 
by  the  chemical  alteration  of  clay  iron-stone,  under  the 
influence  of  air  and  water,  for  it  contains  carbonate  of  iron 
associated  with  clay,  and  with  the  red  oxide  of  iron,  which 
is  formed  by  the  action  of  air  upon  the  carbonate.  Since 
the  Northamptonshire  ore  contains  much  phosphorus  (in 
the  form  of  phosphoric  acid),  it  yields  an  inferior  iron. 

Iron  Pyrites*  is  the  yellow  substance,  of  metallic  appear 
ance,  which  is  so  common  in  lumps  of  coal,  and  may  be 
found  in  rusty  globular  masses  on  the  sea-beach.  It  is  com 
posed  of  46  J  parts  of  iron  in  chemical  combination  with  53^- 
parts  of  sulphur,  and  is  extensively  used  as  a  source  of  sulphur 
in  the  manufacture  of  sulphuric  acid.  Attempts  have  been 
made  to  extract  iron  from  this  mineral  after  the  sulphur 
has  been  burnt  off,  and  the  iron  is  left  in  combination 
with  oxygen  from  the  air,  but  they  have  not  been  attended 
with  much  success.  Since  crystals  of  iron  pyrites  are  found, 
not  only  in  coal,  but  in  many  iron  ores,  it  is  the  chief 
source  of  the  sulphur  which  is  the  most  objectionable  im 
purity  in  iron. 

EXTRACTION    OF    IRON    FROM    ITS    ORES. 

The  difficulty  of  separating  the  iron  from  the  other  sub 
stances  with  which  it  is  associated  in  the  ere,  is  of  course 
greater  in  proportion  as  these  foreign  matters  are  more 
numerous ;  thus,  when  the  iron  is  combined  with  oxygen 
only,  as  in  the  magnetic  iron  ore,  red  haematite,  and  specu 
lar  iron  ore,  the  metal  may  be  extracted  at  once  in  the 
form  of  malleable  iron,  by  merely  heating  the  ore  in  contact 
with  carbon  (charcoal),  which  combines  with  the  oxygen  ; 

*  The  word  pyrites  is  derived  from  the  Greek  for  fire,  probably  in 
allusion  to  the  circumstance  that  when  this  mineral  is  heated  it  gives 
off  sulphur,  which  takes  fire. 


Roasting  of  Iron  Ores.  19 

and  this,  which  is'  the  primitive  process  for  obtaining 
wrought  iron,  is  still  followed  in  places  where  the  above 
ores  can  be  readily  obtained,  and  wood  is  abundant  for  con 
version  into  charcoal.  Even  brown  haematite  and  spathic 
ore  can  be  treated  in  a  similar  manner  if  the  water  and  the 
carbonic  acid  which  they  respectively  contain  be  previously 
expelled  by  calcination. 

But  in  the  clay  iron-stones  and  in  blackband,  the  earthy 
matter  (clay,  &c.)  which  is  present  renders  such  a  process 
impracticable,  and  it  is  necessary  to  raise  such  ores  to  a 
much  higher  temperature,  in  contact  with  lime,  to  liquefy 
the  clay,  so  that  it  may  be  separated  from  the  iron;  when 
the  high  temperature  causes  the  iron  to  combine  with  the 
carbon  of  the  fuel,  forming  cast  iron,  from  which  the  carbon 
is  removed  by  a  subsequent  process,  in  order  to  obtain 
wrought  iron. 

Since  clay  iron-stones  and  blackband  are  the  principal 
ores  smelted  in  Great  Britain,  this  is  the  process  generally 
employed  in  this  country. 

Extraction  of  Iron  from  its  Ores  in  the  Form  of  Cast 
Thw.—The  ore  to  be  smelted  is  broken  up  into  lumps 
about  twice  the  size  of  a  fist,  and  in  some  cases  it  is  found 
advantageous  to  prepare  it  for  smelting  by  a  preliminary 
process  of  calcining  or  roasting.  For  this  purpose  the  ore 
is  mixed  with  small  coal,  and  built  up,  on  a  foundation  of 
lumps  of  coal,  into  huge  pyramidal  heaps,  which  are  kindled 
at  the  windward  end,  and  allowed  to  smoulder  for  months, 
being  prolonged,  as  may  be  requisite,  by  fresh  additions  of 
ore  and  fuel  at  the  opposite  extremity.  The  ore  may  be 
calcined  with  an  addition  of  only  one-twentieth  of  its  weight 
of  coal,  if  it  contain,  as  is  the  case  with  blackband,  a  large 
proportion  of  bituminous  or  combustible  matter,  whilst  a 
clay  iron-stone  may  require  as  much  as  one-fifth  of  its  weight 
of  coal.  This  calcination  in  heaps  is  a  very  uncertain  pro 
cess,  on  account  of  the  irregular  distribution  of  the  heat ; 
some  parts  of  the  ore  being  scarcely  affected,  whilst  others 


C   2 


2O        Metals :  their  Properties  and  Treatment. 

are  over-heated  and  melted  so  that  they  can  be  smelted 
only  with  difficulty.  This  plan  is  only  adopted  in  districts 
where  fuel  is  very  cheap. 

During  the  process  of  calcination  the  ore  loses  about  one- 
fourth  in  weight,  in  consequence  of  the  expulsion  of  water 
and  carbonic  acid,  and  the  combustion  of  the  bituminous 
matter. 

A  portion  of  the  sulphur  from  the  pyrites  contained  in 
the  ore  is  also  burnt  off  during  the  roasting  process,  entering 
into  combination  with  oxygen  from  the  air,  to  form  sulphurous 
acid  gas. 

Many  ores  are  rendered  much  more  porous  by  this  process, 
and  are  then  more  readily  smelted. 

The  expulsion  of  water  and  carbonic  acid  would,  of  course, 
be  effected  by  the  heat  of  the  smelting  furnace  if  this  pre 
liminary  roasting  were  omitted ;  but  the  sulphur  would  not 
be  removed  to  the  same  extent,  and,  since  this  is  one  of  the 
most  damaging  impurities  in  iron,  the  roasting  is  a  necessary 
preparation  for  ores  containing  much  pyrites,  and  is  always 
practised  in  Scotland. 

During  the  calcination  of  the  ore,  the  oxygen  of  the  air 
combines  with  the  protoxide  of  iron  (ferrous  oxide)  which  is 
contained  in  it,  converting  it  into  the  sesquioxide  (ferric 
oxide),  which  is  less  liable  to  enter  into  combination  with 
the  silica  present  in  the  ore,  and  thus  to  cause  a  loss  of  iron 
in  the  slag  during  the  subsequent  smelting  process. 

In  South  Wales  the  ore  is  roasted  in  furnaces  resembling 
lime-kilns,  into  which  it  is  thrown  at  the  top,  alternately 
with  layers  of  small  coal,  the  roasted  ore  being  raked  out  at 
the  bottom  of  the  furnace. 

Calcination  has  been  much  less  practised  since  the  intro 
duction  of  the  hot  blast. 

Process  of  smelting*  Iron  Ores. — Since  this  operation  re 
quires  a  very  high  temperature,  it  is  carried  out  in  a  blast 
furnace,  which  does  not  depend  upon  the  draught  of  a 

*  From  the  German  schmelzent  to  melt. 


The  Blast  Furnace. 


21 


chimney,  but  has  a  strong  blast  of  air  forced  into  it  from 
beneath. 

This  blast-furnace  varies  much  in  form  and  dimensions, 


FIG.  i. — Blast-furnace  for  Smelting  Iron  Ores. 

according  to  circumstances,  which  will  be  better  understood 
when  the  smelting  process  has  been  described.  Fig.  i  shows 
a  common  form,  and  exhibits  the  essential  features  of  its 
construction. 


22         Metals:  tJieir  Properties  and  Treatment, 


The  chimney,  or  tunnel-head  F,  has  three  openings  at  the 
side,  closed  by  iron  doors,  through  which  the  ore  and  fuel 
are  introduced  into  the  furnace,  when  they  fall  through  the 
throat  or  tunnel-hole  G,  into  the  body  c,  which  is  generally  of 
a  barrel-shaped  form,  widening  as  it  descends,  and  thus 
allowing  a  free  descent  of  the  materials  until  they  reach  the 
boshes  A,  after  which  the  furnace  contracts  rapidly,  as  at  B, 
in  order  somewhat  to  check  the  descent  of  the  solid  materials, 
and  attains  its  smallest  diameter  at  the  top  of  the  hearth  E, 
which  is  at  its  upper  part  a  nearly  cylindrical  passage,  but 
is  made  almost  rectangular  at  the  lower  part,  into  which, 

through  apertures  oo  in  the 
walls,  a  blast  of  air  is  forced. 
The  blast-pipes,  or  tuyeres, 
are  usually  three  in  number, 
and  are  situated  on  three 
sides  of  the  hearth.  The 
fourth  side  is  constructed  dif 
ferently  from  these  three,  its 
upper  part  being  formed  by  a 
heavy  block  of  stone  a  (Fig.  2), 
called  the  tymp-stone,  which 
is  supported  by  a  cast-iron 
tymp-plate  b,  built  into  the 
masonry  of  the  furnace,  whilst 
the  lower  part  is  enclosed  by 
the  dam-stone  c,  faced  externally  with  a  thick  cast-iron 
dam-plate  d.  That  portion  of  the  hearth  which  is  shut  in 
by  the  dam-stone  is  called  the  crucible,  for  it  is  here  that 
the  cast  iron  produced  in  the  furnace  accumulates,  in  a 
melted  state,  covered  with  a  layer  of  melted  earthy  matter 
or  slag*  The  space  between  the  tymp  and  dam  stones  is 
rammed  up  with  good  binding  sand,  in  which  an  opening  is 
made,  just  above  the  dam-stone,  through  which  the  slag 


FIG.  2. — Boshes,  Hearth,  and  Crucible 
of  Blast-furnace. 


*  From  the  German  Schlacke,  dross. 


77/6"  Blast  Furnace.  23 

is  allowed  to  flow  out  of  the  furnace.  The  melted  cast  iron 
is  never  permitted  to  rise  to  the  level  of  this  opening,  but  is 
run  out  once  or  twice  in  twenty-four  hours  through  a  tap-hole 
at  the  bottom  of  the  crucible,  which  is  rammed  up  again 
with  binding  sand. 

The  dimensions  of  blast-furnaces  vary  much  according  to 
the  conditions  of  their  working,  but  some  idea  of  them  may 
be  acquired  from  the  following  : — 

Height  of  the  blast-furnace,  from  45  ft.  to  100  ft. 

Height  of  boshes  from  commencement  of  hearth,  about  15  ft. 

Greatest  diameter  at  the  boshes,  from  13  ft.  to  18  ft. 

Diameter  of  chimney  at  charging-platform,  about  IO  ft. 

Diameter  of  hearth,  3  ft.  to  9  ft. 

Depth  of  crucible,  from  8  to  10  inches. 

Total  depth  of  hearth,  6  ft.  to  8  ft. 

Depth  from  tuyere  holes  to  bottom  of  hearth,  from  12  to  36  inches. 

When  the  coal  and  ore  are  soft,  and  easily  crushed,  they 
are  liable  to  obstruct  the  passage  of  the  blast  if  there  be  too 
much  pressure  from  the  column  of  material  above,  so  that 
the  furnace  must  not  be  so  high  as  when  harder  materials  are 
employed.  But  in  such  a  case,  the  diameter  of  the  hearth 
and  body  of  the  furnace  may  be  increased,  whereas  when 
hard  ores  and  anthracite  coal  are  employed,  the  diameter 
must  be  reduced,  sometimes  to  one-half,  and  the  height  in 
creased.  The  compression  caused  by  the  weight  of  materials 
in  the  furnace  sometimes  amounts  to  one-fourth  of  the  bulk 
of  the  charge,  so  that  7,500  cubic  feet  of  materials  measured 
in  the  charging  barrows  may  be  thrown  into  a  furnace  of 
6,000  cubic  feet  in  capacity. 

The  tuyeres,*  or  twyers,  through  which  the  blast  of  air  is 
forced  into  the  furnace,  are  formed  of  conical  tubes  of  cast 
iron  (abdc,  Fig.  3),  having  double  walls  between  which 
water  is  introduced  through  the  pipes  /  /',  and  made  to  cir 
culate  as  shown  by  the  arrows,  in  order  to  keep  them  from 
being  melted.  They  are  between  2  and  3  inches  wide 

*  From  the  French  tuyau,  a  pipe. 


24        Metals :  their  Properties  and  Treatment. 


FIG.  3. — Tuyere  of  Blast-furnace. 


at  the  opening  into  the  furnace,  and  are  built  into  the  walls, 
as  shown  in  Fig.  4,  which  represents  a  section  of  the  hearth 

at    the    level     of     the 
\f  tuyeres.     The  openings 

are  inclined  somewhat 
in  different  directions, 
so  that  the  blasts  com 
ing  from  them  shall  not 
exactly  meet  each  other. 
The  air  is  forced  into 

the  tuyere  through  a  movable  nozzle  (B,  Fig.  3)  of  copper 
or  sheet-iron,  connected  by  a  leathern  hose  (A)  with  the 
pipe  coming  from  the  blowing  machine,  which  is  a  large 

forcing  pump  \vorked 
by  steam  power,  and 
capable  of  supplying 
air,  at  the  rate  of  from 
4,000  to  10,000  cubic 
feet  per  minute  to 
each  furnace. 

The  pressure  of  the 
blast  as  it  issues  into 
the  furnace  usually 
amounts  to  2 Jibs,  or 
3  Ibs.  upon  the  inch, 
but  it  is  sometimes 
increased  to  5  Ibs.  In 
charcoal  furnaces,  the 
fuel  being  very  porous, 
a  pressure  of  i  Ib. 
upon  the  inch  is  suf 
ficient;  in  furnaces  fed 
with  coke,  about  3  Ibs. 
upon  the  inch ;  but  where  anthracite  is  employed,  the  blast 
has  a  pressure  of  4  Ibs. 

When  a  blast  of  high  pressure  is  employed,  it  becomes 


FIG.  4. — Arrangement  of  Tuyeres  in  Blast 
furnace,  t,  Pipes  conveying  the  blast. 
o,  Openings  in  the  sides  of  the  hearth  D. 
R,  Arched  passages  for  the  labourers. 


The  Hot  Blast.  25 

necessary  to  stop  up  the  space  between  the  tuyere  and  the 
nozzle  of  the  pipe  conveying  the  blast. 

The  elbow-pipe,  which  connects  the  blast-pipe  with  the 
air  main  (Fig.  4),  has  usually  a  small  peep-hole  closed  with 
glass  or  mica,  so  that  the  temperature  of  the  hearth,  as  indi 
cated  by  the  colour  of  its  glow,  may  be  observed  by  looking 
through  the  tuyere. 

In  some  modern  furnaces  the  number  of  tuyeres  has  been 
much  increased.  Rachette's  blast-furnace,  which  is  used  in  the 
iron-works  of  the  Ural  for  smelting  magnetic  ore,  and  yields 
30  tons  of  iron  in  24  hours,  is  a  furnace  of  a  narrow  oblong 
section,  with  eight  tuyeres  on  each  side.  It  widens  as  it 
ascends,  unlike  the  older  blast  furnace,  so  that  the  width  is 
greatest  at  the  mouth,  which  causes  the  charge  to  sink  more 
uniformly  in  horizontal  layers. 

When  the  air  is  blown  into  the  furnace  at  the  ordinary 
temperature  of  the  atmosphere,  it  is  spoken  of  as  a  cold-blast 
furnace,  whilst  a  hot-blast  furnace  is  one  in  which  the  air  is 
heated  to  500°  or  600°  F.  (about  the  melting  point  of  lead), 
by  being  forced  through  a  considerable  length  of  red-hot  iron 
pipes,  before  it  enters  the  furnace. 

At  first  sight  it  would  appear  to  be  immaterial  whether 
the  blast  of  air  be  heated  before  or  after  it  is  forced  into  the 
fire,  since,  in  either  case,  the  same  quantity  of  heat  must  be 
lost  in  raising  the  air  to  the  temperature  of  the  fire  itself, 
whether  a  part  of  this  heat  be  produced  by  fuel  burnt  in 
order  to  warm  the  iron  pipes,  or  the  whole  of  it  be  produced 
by  fuel  consumed  in  the  furnace.  In  the  stoves  for  heating 
the  blast,  however,  the  carbon  of  the  fuel  is  converted  into 
carbonic  acid,  whilst  in  the  blast-furnace  it  is  converted  into 
carbonic  oxide,  combining,  in  the  latter  case,  with  only  half 
as  much  oxygen  as  in  the  former,  and  producing  less  than 
one-third  as  much  heat,  so  that  2  cwt.  of  coal  burnt  in  the 
stove  will  go  as  far  as  above  7  cwt.  burnt  in  the  furnace. 
Moreover,  when  cold  air  is  blown  into  the  furnace,  it  must 
pass  through  a  much  larger  quantity  of  the  heated  fuel  before 


26        Metals :  their  Properties  and  Treatment. 

it  is  raised  to  the  temperature  of  the  fire  than  would  be  the 
case  if  it  had  been  heated  before  entering,  so  that  the  hot 
blast  has  less  cooling  effect  upon  the  fire,  and  a  much  higher 
temperature  may  be  produced  by  the  same  consumption  of 
fuel,  or  a  fire  sufficiently  hot  for  smelting  the  iron  ore  may  be 
raised  with  a  smaller  consumption  of  fuel  than  when  a  cold 
blast  is  employed.  The  economy  of  fuel  is  still  greater 
when  the  blast  is  heated  without  any  extra  expenditure  of 
fuel,  by  employing  the  waste  heat  derived  from  the  furnace 
itself. 

An  improved  method  of  heating  the  blast  consists  in 
employing  two  chambers  of  fire-brick,  in  which  fire-bricks 
are  loosely  stacked.  Into  each  of  these  chambers,  alter 
nately,  the  flame  of  a  coal  fire  is  passed  until  the  bricks  are 
heated  to  redness  ;  the  fire  is  then  diverted  into  the  other 
chamber,  whilst  the  blast  is  sent  over  the  hot  bricks,  when 
it  becomes  heated  to  1,300°  F.  before  entering  the  blast 
furnace.  By  the  time  this  chamber  has  been  cooled,  the 
other  is  heated  and  ready  to  do  duty  again.  These  regenera 
tive  stoves,  as  they  are  called,  have  been  employed,  with 
great  advantage,  in  other  cases. 

In  the  construction  of  the  blast-furnace,  very  infusible 
materials  are  necessary,  especially  in  the  crucible  and 
hearth,  where  the  highest  temperature  prevails.  For  these 
portions  of  the  furnace,  millstone  grit  or  Newcastle  sand 
stone  is  sometimes  employed  (though  fire-brick  has  been 
lately  used),  but  the  upper  part  or  body  of  the  furnace, 
which  is  not  exposed  to  so  high  a  temperature,  is  lined 
either  with  fire-brick,  or  sometimes  with  blocks  of  slag  from 
the  furnace  itself,  which  undergoes  an  alteration  in  structure, 
rendering  it  less  fusible  when  exposed  to  the  heat  of  this 
portion  of  the  fire.  The  fire-brick  lining  (//,  Fig.  i)  of  the 
furnace  is  double,  a  space  of  about  three  inches  being  left 
between  the  two  portions,  and  rammed  up  with  powdered 
coke  or  sand,  which  yields  to  the  expansion  of  the  brick 
work,  and  hinders  the  conduction  of  the  heat  to  the  external 


Lighting  the  Blast  Furnace.  27 

part  of  the  structure.  Much  attention  is  given  to  the  slope 
of  the  boshes,  for  if  this  be  too  steep,  the  materials  will  fall 
too  quickly,  and  if  it  be  not  steep  enough,  they  will  stick 
to  the  sides,  and  form  obstructions  or  scaffolds,  preventing 
the  descent  of  the  materials  above.  Three  or  more  blast 
furnaces  are  generally  built  in  a  row,  and  vaulted  passages 
are  left  around  the  hearth  to  allow  easy  access  to  the  tuyeres 
and  the  crucible.  When  the  masonry  of  the  blast-furnace  is 
slight,  it  is  strengthened  by  iron  hoops  and  bars  (cupola  fur 
nace),  or  it  is  sometimes  cased  externally  with  boiler-plates 
riveted  together. 

The  fuel  of  blast-furnaces  in  this  country  is  almost  ex 
clusively  coal  or  coke,  for  charcoal  is  far  too  expensive  for 
general  use,  though  its  freedom  from  sulphur  enables  a  better 
quality  of  iron  to  be  manufactured  with  it.  In  Austria,  char 
coal  from  wood  or  peat  is  the  only  fuel  employed,  and  iron 
of  the  finest  quality  is  the  result.  The  Swedish  iron  works 
also  use  charcoal  only. 

In  hot-blast  furnaces,  coal  may  be  employed  without  hav 
ing  been  coked,  because  the  higher  temperature  which  pre 
vails  in  the  furnace  allows  it  to  become  converted  into  coke 
in  the  upper  part  of  the  fire  ;  but  for  cold-blast  furnaces,  coke 
is  the  ordinary  fuel,  a  hard-burnt  dense  quality  being  preferred. 

For  lighting  or  putting  the  furnace  in  blast,  much  time  is 
required,  since  there  would  be  great  danger  of  cracking  the 
lining  by  a  sudden  application  of  a  very  high  temperature. 
Before  the  dam-stone  is  fixed  in  its  place,  faggots  are  kindled 
in  the  opening  below  the  tymp-stone,  so  that  the  flame  and 
heated  air  may  be  drawn  up  into  the  furnace  and  gradually 
warm  it.  After  a  few  days,  a  quantity  of  coal  or  coke  is 
thrown  in  at  the  throat  of  the  furnace,  and  gradually  in 
creased  until  the  furnace  is  filled  ;  the  blast  is  then  gradually 
turned  on,  and  when  the  fuel  has  sunk  down  sufficiently,  the 
smelting  operation  is  commenced.  This  drying  and  warm 
ing  of  the  furnace  occupy  a  month  or  more,  according  to 
its  size. 


28        Metals :  their  Properties  and  Treatment. 

For  the  convenience  of  charging  the  furnace  with  fuel  and 
ore,  a  gallery  runs  round  it  at  the  level  of  the  tunnel-hole, 
to  which  the  materials  are  brought  in  iron  waggons  or  bar 
rows,  either  up  an  inclined  plane,  or  along  a  tramway  carried 
from  the  slope  over  against  the  furnace. 

From  3  to  6  cwt.  of  iron  ore,  according  to  its  richness,  is 
thrown  on  to  the  top  of  the  burning  fuel,  together  with 
about  one-third  of  its  weight  of  limestone  or  of  quick  lime, 
which  is  employed  as  &flux*,  to  bring  the  clay  of  the  ore  to 
a  liquid  state  in  the  fire,  in  order  that  it  may  be  separated 
from  the  iron.  Upon  this  a  charge  of  fuel  is  thrown,  consist 
ing  of  about  4  or  6  cwt.  The  descent  of  the  charge  in  the 
furnace  is  very  gradual,  from  40  to  50  hours  being  usually 
occupied  in  its  passage  from  the  top  to  the  bottom. 

After  an  interval  of  half  an  hour  or  so,  fresh  charges  of  ore, 
flux,  and  fuel  are  introduced,  and  the  furnace  is  thus  fed, 
night  and  day,  for  six  or  seven  years,  before  it  is  found 
necessary  to  blow  it  out  in  order  that  its  lining  may  be 
repaired. 

The  melted  cast  iron  which  is  produced  runs  down  into 
the  crucible,  together  with  the  liquid  slag,  formed  by  the 
action  of  the  lime  in  the  flux  upon  the  clay  in  the  ore.  The 
cast  iron,  being  the  heavier  of  the  two,  accumulates  at  the 
bottom,  and  above  it,  five  or  six  times  its  bulk  of  liquid  slag, 
which  flows  out  over  a  notch  in  the  dam-plate,  and  is  gene 
rally  received  in  iron  moulds  and  cast  into  large  blocks  of 
15  or  20  cwt.  each. 

At  intervals  of  twelve  hours,  generally,  the  furnace  is 
tapped  by  opening  the  tap-hole  with  an  iron  rod,  and  a  cast 
is  made,  that  is,  the  liquid  cast  iron  is  run  out  and  cast  into 
pigs,  or  rough  half-round  bars,  either  in  thick  iron  moulds, 
or  in  trenches  excavated  in  strongly  binding  sand,  and  com 
municating  with  a  central  channel  into  which  the  cast  iron 
flows  from  the  furnace.  The  pigs  of  iron  are  about  three 

*  From  the  Latin  fluo,  to  flow. 


29 


Tapping  the  Blast  Furnace. 


feet  long  and  four  inches  in  diameter,  and  weigh 
About  five  or  six  tons  are  usually  run  out  at  each  tapping. 
The  foundry  iron  intended  for  the  manufacture  of  castings 


FIG.  5. — Hot-Blast  Furnace  for  Smelting  Iron  Ores  ;  showing,  on  the  right, 
the  stove  for  heating  the  blast  ;  on  the  left,  the  large  air-chamber  or 
regulator  for  equalising  the  blast.  In  front  are  seen  the  slag-moulds  on 
a  tramway,  and  the  channel  through  which  the  cast  iron  is  conducted 
into  the  pig-moulds. 

is  generally  run  into  sand-moulds;  but/or^?  iron,  which  is  to 
be  afterwards  converted  into  wrought  iron,  is  cast  in  iron 
moulds,  partly  to  avoid  contamination  with  the  sand,  and 


3O         Metals :  their  Properties  and  Treatment. 

partly  to  render  the  metal  brittle,  so  that  it  may  be  easily 
broken  up  for  the  puddling  process  which  it  next  undergoes. 

The  blast  is  suspended  during  the  operation  of  tapping, 
and  turned  on  again  at  the  end,  in  order  to  force  all  the  iron 
and  slag  out  of  the  hearth.  Fig.  5  exhibits  a  general  view  of 
the  arrangements  connected  with  a  blast-furnace. 

Chemical  Changes  which  take  place  in  the  Blast-furnace. — 
The  great  variety  of  the  substances  present  in  the  blast 
furnace  causes  the  chemical  reactions  to  be  too  numerous 
and  elaborate  to  be  fully  considered  except  in  a  purely 
chemical  treatise ;  but  the  principal  changes  which  result  in 
the  production  of  cast  iron  and  slag  from  the  ore,  flux  and 
fuel  can  be  easily  understood. 

The  iron  being  contained  in  the  ore  in  the  state  of  oxide, 
that  is,  in  chemical  combination  with  oxygen,  this  element 
must  be  removed  in  order  to  obtain  the  iron  in  the  metallic 
state.  The  whole  of  the  iron  would  thus  be  easily  reduced 
by  the  combustible  gases  in  the  furnace,  if  the  ore  consisted 
of  oxide  of  iron  only,  but  the  presence  of  clay  in  the  iron 
stone  introduces  a  difficulty.  Clay  consists  of  alumina  and 
silica,  and  cannot  be  melted  alone,  even  in  the  blast-furnace. 
In  contact  with  oxide  of  iron,  however,  the  clay  combines 
chemically  with  that  substance,  and  melts  to  a  liquid  which 
becomes  a  black  glass  or  slag  when  it  cools.  The  greater 
part  of  the  iron  would  thus  be  lost  in  the  slag.  But  if  a 
quantity  of  lime  be  mixed  with  the  ore,  the  clay  will  combine 
with  it  instead  of  combining  with  the  oxide  of  iron,  which 
can  then  be  made  to  yield  the  whole  of  its  metal.  The  lime 
is  sometimes  put  into  the  furnace  in  the  form  of  limestone 
or  carbonate  of  lime,  and  sometimes  in  that  of  quicklime,  or 
limestone  from  which  the  carbonic  acid  has  been  expelled 
by  heat.  The  use  of  quicklime  not  only  avoids  the  local 
loss  of  heat  necessary  to  expel  the  carbonic  acid  from  the 
limestone,  but  it  increases  the  production  of  iron,  because  it 
occupies  a  smaller  space  than  the  limestone,  and  allows 
more  charges  to  pass  through  the  furnace  in  a  given  time. 


Chemical  Changes  in  the  Blast  Furnace.          3 1 

The  air  which  is  blown  in  at  the  bottom  of  the  furnace 
contains  one  part  by  measure  of  oxygen  mixed  with  four 
measures  of  nitrogen.  When  it  comes  into  contact  with  the 
glowing  carbon  of  the  fuel,  the  latter  combines  chemically 
with  the  oxygen,  forming  carbonic  acid  gas,  which  contains 
eight  parts  by  weight  of  oxygen  combined  with  three  parts  of 
carbon ;  but  as  this  gas  passes  up  the  furnace,  it  gives  up  one 
half  of  its  oxygen  to  another  portion  of  the  heated  carbon, 
and  becomes  carbonic  oxide  gas,  which  contains  four  parts 
by  weight  of  oxygen  combined  with  three  parts  of  carbon. 
Still  passing  upwards  through  the  furnace,  the  carbonic  oxide 
meets  the  red-hot  ore  containing  oxide  of  iron,  from  which 
it  regains  the  oxygen  necessary  to  convert  it  into  carbonic 
acid,  thus  reducing  the  iron  to  the  metallic  state.  Continuing 
its  ascent,  this  carbonic  acid  traverses  more  red-hot  carbon, 
and  is  again  converted  into  carbonic  oxide,  in  which  form  it 
issues  from  the  chimney  of  the  furnace,  accompanied  by  the 
nitrogen  of  the  air  and  by  smaller  quantities  of  other  gases 
produced  in  the  furnace. 

The  metallic  iron,  which  has  been  separated  from  the 
oxygen  during  the  passage  of  the  carbonic  oxide  over  the 
heated  ore,  is  not  capable  of  being  melted  at  the  temperature 
of  this  furnace  until  it  has  combined  chemically  with  some 
of  the  carbon  which  surrounds  it,  and  has  thus  become 
converted  into  cast  iron,  which  is  then  liquefied  by  the  heat 
and  runs  down  into  the  crucible  of  the  furnace,  accompanied 
by  the  melted  slag  formed  by  the  combination  of  the  lime 
in  the  flux  with  the  clay  contained  in  the  ore. 

The  chief  chemical  operations  taking  place  in  the  blast 
furnace  may  therefore  be  summed  up  as  follows  :— 

1.  Combination  of  oxygen  from  the  air  with  carbon  from 

the  fuel  to  form  carbonic  add. 

2.  Conversion  of  carbonic  acid  into   carbonic  oxide  by 

giving  up  half  its  oxygen  to  red-hot  carbon. 

3.  Conversion  of  oxide   of  iron   into   metallic   iron   by 

parting  with  its  oxygen  to  heated  carbonic  oxide. 


32        Metals :  their  Properties  and  Treatment. 


4.  Combination  of  metallic  iron  with  carbon  to  form  cast 

iron. 

5.  Combination  of  lime  with  clay  (silica  and  alumina)  to 

form  a  glass  or  slag. 

Employment  of  the  waste  Gas  from  the  Blast-furnace. — The 
gas  which  issues  from  the  chimney  of  the  furnace  contains, 
beside  the  carbonic  oxide,  considerable  quantities  of  other 
combustible  gases  produced  by  the  action  of  heat  upon  the 
coal  when  that  fuel  is  employed,  and  of  hydrogen  derived 
from  the  decomposition  of  the  water  present  in  the  air  and 
in  the  solid  materials.  This  gas 
was  formerly  allowed  to  burn  in  the 
air  as  it  escaped  from  the  chimney, 
and  its  flame,  coloured  yellow  and 
red  by  minute  quantities  of  vapour 
of  sodium  and  calcium,  illuminated 
the  sky  in  the  iron  districts.  But 
within  the  last  thirty  years  the  waste 
gases  have  been  turned  to  more  use 
ful  account.  Openings  aa  are  some 
times  made  in  the  sides  of  the  fur 
nace  A,  as  shown  in  Fig.  6,  at  about 
four  feet  below  its  mouth,  through 
which  the  gases  mid  an  easier 
escape  than  through  the  mass  of 
fuel  and  ore  above,  and  pass  into 
flues,  whence  they  are  conducted  by  iron  pipes  b  into  kilns, 
where  they  are  used  as  fuel  for  calcining  the  ore  or  the  lime 
stone  flux. 

In  order  to  allow  the  waste  gas  to  be  drawn  off  more 
completely,  the  mouth  of  the  furnace  is  sometimes  provided 
with  a  hopper,  as  shown  in  Fig.  7,  the  lower  part  of  which  is 
closed  by  an  inverted  cone  of  sheet  iron,  suspended  by  a 
chain  from  one  end  of  a  lever  and  balanced  by  a  weight  at 
the  other.  When  the  charge  is  thrown  into  the  hopper  the 
cone  descends  and  the  materials  fall  into  the  furnace,  after 


FIG.  6. — Blast-furnace,  with 
openings  for  drawing  off 
the  waste  gases. 


Use  of  Waste  Gases  from  Blast  Furnace.         33 

which  the  cone  returns  to  its  former  position,  closing  the 
hopper,  and  allowing  the  waste  gas  to  pass  off  through 
the  flue. 

At  Ulverstone  the  waste  gases  are  drawn  off  through  an 
iron  pipe  about  three  feet  wide,  which  descends  six  feet  into 
the  furnace,  and  is  supported  by  brickwork  projections. 
(Fig.  8.)  Exhausting  fans  are  employed  to  draw  the  gases 
through  the  furnaces  in  which  their  combustion  is  effected. 
The  pipe,  being  placed  in  the  centre  of  the  throat  of  the 


FIG.  7.-Cup  and  Cone  for  closing  the  Blast-furnace,  in  order  that  the  waste  gases 
may  pass  into  the  lateral  flue,  as  shown  by  the  arrow. 

furnace,  leaves  an  interval  of  about  four  feet  all  round  it, 
for  the  introduction  of  the  charge,  which  is  thus  equally  dis 
tributed. 

The  large  proportion  of  carbonic  oxide  present  in  the  gas 
escaping  from  the  blast-furnace,  renders  it  very  poisonous, 
and  it  has  occasionally  caused  the  death  of  persons  engaged 
in  tending  the  furnace. 

Although  by  far  the  greater  part  of  the  nitrogen  contained 
in  the  air  blown  into  the  furnace  undergoes  no  chemical 


34        Metals :  their  Properties  and  Treatment. 


change,  but  escapes  unaltered  in  the  waste  gases,  a  small 
proportion  of  it  appears  to   enter   into   combination  with 

carbon,  and  with  the  potas 
sium  which  is  present  in  the 
materials  composing  the 
charge,  to  form  the  cyanide 
of  potassium,  which  has  been 
obtained  in  considerable 
quantity  from  some  furnaces. 
Beautiful  copper-coloured 
crystals  are  not  uncommonly 
found  in  the  hearth  of  the 
furnace,  consisting  of  a  com 
pound  of  nitrogen  with  car 
bon  and  titanium,  this  metal 
being  derived  from  the  titanic 
acid  which  is  frequently  pre 
sent  in  the  ores  of  iron. 

As  might  be  expected,  the 
composition  of  the  gas  issu 
ing  from  the  furnace  varies 
considerably;  but  the  sub 
joined  analysis  of  a  sample, 
taken  from  a  furnace  in  which 
coal  was  the  fuel  employed, 
will  illustrate  its  general 
nature. 


FIG.  8. — Schneider's  arrangement  for 
collecting  the  waste  gases  from  the 
Blast-furnace  by  a  central  pipe. 


Gas  from  Blast  Furnace. 


Nitrogen  . 
Carbonic  Oxide 
Hydrogen 
Carbonic  Acid 
Marsh  Gas 
Olefiant  Gas     . 


55  vols. 
26     „ 

7  >, 

8  „ 

3: 


100 


Blast-furnace  Slag.  35 

Composition  of  the  Slag  or  Cinder  from  the  Blast-furnace. — 
The  slag  which  runs  out  of  the  furnace  solidifies  on  cooling 
to  an  opaque  glassy  mass,  in  various  shades  of  grey,  blue, 
green,  brown,  and  black,  sometimes  prettily  striped  and 
variegated.  It  consists  essentially,  as  already  noticed,  of 
the  constituents  of  clay,  viz.  silica  and  alumina,  united  with 
lime,  and  the  presence  of  these  three  substances  in  the  fur 
nace  is  necessary  for  the  production  of  a  liquid  slag.  In 
order  to  secure  this,  both  the  quality  and  quantity  of  the 
earthy  matter  or  gangue  *  associated  with  the  ore  must  be 
taken  into  account.  When  clay,  which  contains  both  silica 
and  alumina,  is  present,  lime  will  form  an  appropriate  flux  ; 
but  if  limestone  only  were  contained  in  the  ore,  an  addition 
of  clay  would  be  requisite  ;  again,  ores  in  which  the  gangue 
consisted  of  quartz  (silica)  would  require  the  addition  of 
alumina  (in  the  form  of  clay)  as  well  as  lime.  In  some  cases 
it  is  found  possible  to  mix  the  different  ores  so  that  the 
clay  associated  with  one  may  form  a  slag  with  the  lime 
contained  in  another,  rendering  it  unnecessary  to  add  any 
other  flux. 

In  order  that  clay  and  lime  may  easily  melt  together  into 
a  glass,  the  lime  should  be  rather  more  than  one-third  of 
the  weight  of  the  clay;  and  since  limestone  (or  carbonate  of 
lime)  contains  somewhat  more  than  half  its  weight  of  lime, 
two  parts  of  limestone  should  be  employed  for  three  of  clay. 
In  furnaces  where  coal  or  coke  is  burnt,  it  is  usual  to  employ 
rather  more  lime  than  this,  because  it  hinders  the  sulphur 
from  passing  into  the  iron ;  for  lime  consists  of  the  metal 
calcium  in  chemical  combination  with  oxygen,  which  is 
removed  by  the  strongly-heated  carbon,  leaving  the  calcium 
free  to  unite  with  the  sulphur,  forming  a  sulphide  or  snl- 
phuret  of  calcium,  which  is  found  in  the  slag.  It  is  said 
that  not  only  more  sulphur  but  also  more  silicon  is  found  in 
the  iron  when  less  limestone  is  employed.  An  average 

*  From  the  German  Gang,  a  mineral  vein. 
D  2 


36        Metals :  their  Properties  and  Treatment. 

sample  of  slag  from  the  blast-furnace  gave  the  following 
results  when  analysed  : — 


Slag  from  Blast  Furnace. 

Silica  . 

Alumina 

Lime   . 

Magnesia 

Oxide  of  Iron 

Oxide  of  Manganese 

Potash 

Sulphide  of  Calcium 

Phosphoric  Acid  . 


43-07 
I4-85 
28-2 


i'37 
1-84 
1-90 

trace 

100-35 


The  slag  is  commonly  employed  for  road-making  in  the 
neighbourhood  of  the  iron-works.  Some  attempts  have  been 
made  to  turn  the  slag  to  account  by  employing  it  as  a 
manure  for  soils  deficient  in  potash,  of  which  it  will  be  seen 
that  the  above  slag  contains  nearly  ^th  of  its  weight,  in  a 
form  which  would  be  easily  rendered  available  for  plants  by 
the  combined  action  of  air  and  moisture.  When  the  slag  is-- 
run  into  water,  or  blown  into  a  frothy  condition  by  the 
blast,  it  resembles  pumice-stone,  and  is  easily  ground  to  a 
powder  fit  for  applying  to  the  soil. 

It  might  be  anticipated  that  the  appearance  of  the  slag 
would  convey  to  the  experienced  eye  some  useful  informa 
tion  with  respect  to  the  character  of  the  ore  and  the  general 
progress  of  the  smelting  operation.  A  good  slag  is  liquid, 
nearly  transparent,  of  a  light  grey  colour,  and  has  a  fracture 
somewhat  resembling  that  of  limestone.  A  dark  slag  shows 
that  much  of  the  oxide  of  iron  is  escaping  unreduced. 
Streaks  of  blue  are  commonly  found  when  ores  containing 
sulphur  are  being  smelted,  possibly  from  the  presence  of  a 
substance  similar  to  ultramarine,  the  constituents  of  which 
are  all  present  in  the  slag.  Again,  the  slags  obtained  in 
smelting  ores  containing  titanium  generally  present  a  pecu 
liar  blistered  appearance.  The  connection  between  the 


Composition  of  Cast  Iron,  37 

character  of  the  slag  and  that  of  the  cast  iron  obtained  at 
the  same  time  will  be  particularly  noticed  hereafter. 

Some  of  the  slag  usually  accumulates  in  front  of  the 
nozzles  of  the  tuyeres,  where  it  is  chilled  by  the  blast,  and 
forms  a  conical  prolongation  of  the  pipe,  which  is  useful  in 
directing  the  blast  into  the  centre  of  the  furnace  instead  of 
allowing  it  to  pass  up  the  sides.  But  occasionally  these 
noses  of  slag  meet  in  the  middle  and  obstruct  the  blast  in  a 
very  serious  manner.  The  proportion  between  the  iron  and 
the  slag  is  of  some  importance;  for  if  the  volume  of  the 
latter  be  too  small,  it  will  not  suffice  tc*  protect  the  metal 
from  the  action  of  the  oxygen  in  the  blast,  and  much  waste 
of  iron,  in  the  form  of  oxide,  will  result. 

The  slag  should  require  about  the  same  temperature  to 
melt  it  as  the  cast  iron;  for  if  it  be  too  fusible,  a  part  of  the 
oxide  of  iron  contained  in  the  ore  may  be  dissolved  in  it 
and  escape  reduction  to  the  metallic  state. 

CAST    IRON. 

The  only  substance  with  which  the  iron  is  invariably  and 
indispensably  associated  in  cast  iron  is  carbon,  so  that  it  has 
sometimes  been  spoken  of  as  a  carbide  or  carburet  of  iron. 
But  this  would  convey  the  impression  that  the  whole  of  the 
iron  present  existed  in  chemical  combination  with  the 
carbon,  exactly  as,  in  the  oxide  of  iron,  the  whole  of  the 
iron  is  combined  with  oxygen,  whereas  the  greater  part  of 
the  iron  in  cast  iron  is  present  in  the  uncombined  state,  its 
properties  being  altered  or  modified  by  the  presence  of  the 
carbide  of  iron  (or  compound  of  carbon  with  iron)  which  is 
diffused  throughout  the  metal.  But  for  the  circumstance 
that  the  term  alloy  is  conventionally  restricted  to  the  sub 
stances  formed  by  the  alliance  of  metals  with  each  other,, 
whilst  carbon  is  a  non-metallic  body,  cast  iron  might  be 
appropriately  designated  an  alloy  of  iron  with  carbon. 

By  fusing  finely  divided  iron  with  charcoal  until  the 
metal  has  taken  up  as  much  carbon  as  it  will  dissolve,  a 


38         Metals :  their  Properties  and  Treatment. 

dark  grey  mass  is  obtained,  which  is  so  brittle  that  it  may  be 
powdered  in  a  mortar.  This  substance  appears  to  be  a 
chemical  compound  of  carbon  with  iron,  or  a  carbide  (car 
buret)  of  iron,  containing,  in  100  parts,  94*36  of  iron,  and 
5-64  parts  of  carbon.  The  proportion  of  carbon  present  in 
cast  iron  varies  in  different  samples,  but  it  never  amounts  to 
5  per  cent.,  so  that  the  carbide  of  iron  must  be  regarded  as 
being  in  a  state  of  intimate  mixture  with  metallic  iron. 

On  examining  the  fracture  of  freshly-broken  pieces  of  cast 
iron,  it  will  be  found  that  some  specimens  have  a  silvery 
white,  and  others  a  grey  colour,  caused  by  the  presence  of 
very  minute  particles  of  carbon,  which  are  interspersed 
among  the  lighter-coloured  particles  of  the  metal.  When  the 
grey  samples  of  cast  iron  are  acted  upon  by  acids  (diluted 
sulphuric  or  hydrochloric)  the  iron  is  dissolved,  but  the 
black  particles  of  carbon  are  left,  and  these  are  found  to 
possess  the  same  properties  as  the  natural  variety  of  carbon 
known  as  black  lead  or  graphite*  of  which  pencils  are  made. 
When  the  white  cast  iron  is  dissolved  in  acids,  very  little 
black  residue  of  carbon  is  left,  because  the  greater  part  of 
the  carbon  is  present  in  the  state  of  chemical  combination 
with  the  iron,  as  a  carbide  of  iron  which  is  dissolved  by  the 
acid,  and  very  little  is  present  in  the  form  of  graphite. 

When  a  sample  of  grey  cast  iron  is  melted,  the  particles  of 
free  carbon  are  dissolved  by  the  liquid  metal,  becoming 
chemically  combined  with  a  portion  of  the  iron ;  and  if  the 
melted  mass  be  suddenly  chilled  by  throwing  water  upon  it, 
or  by  running  it,  when  not  far  from  its  point  of  solidification, 
into  a  thick  iron  mould,  the  carbon  does  not  separate  again, 
so  that  a  mass  of  white  cast  iron  is  thus  produced.  It  is 
more  difficult  to  convert  the  white  into  the  grey  variety  of 
cast  iron,  but  this  has  been  effected  by  exposing  the  melted 
metal  to  a  high  temperature  and  allowing  it  to  cool  down 
very  slowly,  when  a  portion  of  the  carbon  separated  from 
the  iron  and  the  grey  variety  of  cast  iron  was  produced. 

*  Froip  the  Greek  verb,  to  write. 


Varieties  of  Cast  Iron.  39 

These  principles  receive  important  practical  application 
in  the  process  of  chill-casting,  in  which  the  iron  is  cast  in 
thick  iron  moulds  or  chills,  in  order  to  impart  to  it  a  hardness 
rivalling  that  of  steel.  On  the  other  hand,  castings  which 
are  too  hard  to  admit  of  being  turned  or  bored,  are  softened 
by  being  heated  for  several  hours  in  sand,  or  in  a  mixture  of 
coal-dust  and  bone-ash,  being  afterwards  allowed  to  cool 
slowly,  which  is  favoured  by  the  bad  conducting  power  of 
those  materials. 

Since  in  grey  cast  iron  a  smaller  proportion  of  the  iron  is 
in  combination  with  carbon,  and  more  of  it  in  the  true 
metallic  state,  this  variety  would  be  expected  to  exhibit  more 
of  the  properties  of  metallic  iron,  whilst  white  iron  ought  to 
present  the  characters  of  the  chemical  compound  of  carbon 
with  iron,  described  above.  Accordingly,  the  grey  cast  iron 
is  much  softer  than  white  iron,  and  admits  of  being  filed  and 
turned,  whereas  the  white  iron  is  so  extremely  hard  that  a 
file  will  scarcely  touch  it,  and  a  blow  from  a  hammer,  which 
indents  a  pig  of  grey  iron,  will  break  up  one  of  white  iron. 
The  larger  proportion  of  metallic  iron  contained  in  the  grey 
cast  iron  causes  it  to  require  a  higher  degree  of  heat  before 
it  begins  to  exhibit  signs  of  fusion,  but  it  is  capable  of 
becoming  very  liquid  at  a  sufficiently  high  temperature,  so 
as  to  be  easily  run  into  moulds;  white  cast  iron,  on  the 
other  hand,  is  softened  at  a  rather  lower  temperature,  but 
does  not  flow  well,  assuming  a  somewhat  viscid  or  pasty 
consistence.  It  scintillates,  or  throws  off  sparks,  as  it  runs 
from  the  furnace,  to  a  much  greater  extent  than  grey  iron. 
White  cast  iron  is  about  ^th  heavier  than  the  grey  variety, 
its  average  specific  gravity  being  7-5,  whilst  that  of  grey  iron 
is  7-1.  The  grey  iron  rusts  more  easily  in  air,  and  is  more 
readily  acted  on  by  acids,  than  white  iron,  which  may  be 
ascribed  partly  to  its  containing  more  iron  in  an  uncombined 
form,  and  partly  to  the  acceleration  of  chemical  action  caused 
by  the  voltaic  disturbance  excited  by  the  contact  of  the 


40        Metals :  their  Properties  and  Treatment. 

particles  of  graphite  with  the  particles  of  iron,  in  the  presence 
of  the  acid  (in  the  case  of  air,  carbonic  acid). 

White  iron  usually,  but  by  no  means  invariably,  contains 
less  total  carbon  than  grey  iron. 

Mottled  cast  iron  is  composed  of  a  mixture  of  the  grey  and 
white  varieties  in  varying  proportions,  the  grey  iron  some 
times  appearing  in  specks,  like  minute  flowers,  upon  a  white 
ground,  whilst  in  other  specimens  the  mass  is  composed  of 
grey  iron,  and  the  white  iron  appears  in  spots. 

The  tenacity  of  cast  iron  is  found  to  be  increased  by 
remelting,  probably  because  some  of  the  uncombined  carbon 
is  thus  induced  to  combine  with  the  iron. 

Although,  as  stated  above,  carbon  appears  to  be  the  only 
substance  indispensably  associated  with  the  metal  in  cast 
iron,  the  commercial  varieties  of  this  material  always  contain 
silicon,  phosphorus,  sulphur  and  manganese,  which  are  often 
present  in  considerable  proportion,  and  are  known  to  exer 
cise  an  influence  upon  the  character  of  the  cast  iron.  Other 
substances,  such  as  titanium,  cobalt,  nickel,  chromium, 
copper,  vanadium,  calcium,  magnesium  and  arsenic,  may 
also  be  discovered  by  a  careful  analysis  of  considerable 
quantities  of  cast  iron,  but  they  are  generally  present  in 
very  small  proportion,  and  are  not  known  to  produce  any 
effect  upon  the  metal. 

Next  to  the  carbon,  silicon  (or  siliduni)  is  the  commonest 
and  most  abundant  constituent  of  cast  iron,  its  quantity 
varying  from  T^VTTtn  Part  to  nearly  -^th  part  of  the  weight 
of  the  metal,  the  proportion  of  silicon  being  higher  in  the 
grey  than  in  the  white  variety.  The  silicon  appears  to  exist 
in  a  state  of  chemical  combination  with  the  iron,  and  is 
derived  from  the  silica  in  the  ore  or  in  the  fuel.  Silica  is  a 
combination  of  silicon  with  oxygen,  and  when  the  latter  is 
abstracted  by  the  carbon  at  the  high  temperature  of  the 
blast-furnace,  the  silicon  enters  into  combination  with  the 
iron.  The  presence  of  a  large  proportion  of  silicon  in  cast 
iron  is  generally  regarded  as  injurious  to  its  quality,  the 


Manganese  and  Phosphorus  in  Cast  Iron.        41 

strongest  cast  irons  being  those  which  contain  a  small 
quantity  of  that  element.  Iron  which  has  been  smelted 
with  coke  contains  a  larger  proportion  of  silicon  than  that 
smelted  with  charcoal,  and  hot-blast  iron  commonly  contains 
more  than  that  smelted  by  cold-blast. 

Manganese  is  seldom  if  ever  absent  from  cast  iron,  for  it  is 
a  metal  which  very  nearly  resembles  iron  in  its  chemical 
properties,  and  is  commonly  found  in  iron  ores,  so  that  the 
same  operation  which  reduces  the  iron  in  the  blast-furnace 
also  reduces  the  manganese,  and  this  metal  becomes  alloyed 
or  intimately  mixed  with  the  melted  iron.  The  manganese 
has  been  found  in  the  large  proportion  of  -^th  of  the  weight 
of  the  cast  iron,  but  it  seldom  exceeds  ¥Vth.  The  influence 
exerted  by  manganese  upon  the  character  of  the  cast  iron  is 
very  decided,  tending  to  the  production  of  the  white  variety, 
the  manganese  diminishing  the  tendency  of  the  carbon  to 
separate  in  the  form  of  graphite.  White  cast  iron,  therefore, 
is  found  to  contain  the  largest  proportion  of  manganese. 

The  spathic  iron  ores  yield  a  cast  iron  containing  a  par 
ticularly  large  quantity  of  manganese,  sometimes  exceeding 
•j^th  of  the  weight  of  the  cast  iron.  Such  an  iron  is  capable 
of  retaining  upwards  of  -^ th  its  weight  of  carbon  in  chemical 
combination  with  it,  and  the  compound  thus  formed  crys 
tallises  in  large  shining  plates,  whence  it  is  named  by  the 
Germans  Spiegel-risen  or  mirror-iron.  It  is  largely  employed 
in  the  manufacture  of  Bessemer  steel. 

It  has  been  asserted  that  the  presence  of  manganese  in 
iron  ores  encourages  the  passage  of  sulphur  and  silicon  into 
the  slag,  thus  reducing  the  proportion  of  those  injurious 
impurities  in  the  metal. 

Phosphorus  occasionally  forms  between  ^th  and  -^th  part 
of  the  weight  of  cast  iron,  but  about  T-^jth  part  is  a  commoner 
proportion  of  phosphorus.  It  exists  in  chemical  combination 
with  a  portion  of  the  metal,  as  phosphide  of  iron,  and  is 
derived  either  from  phosphate  of  iron  contained  in  the  ore, 
or  from  phosphate  of  lime  which  is  frequently  present  in  the 


42         Metals :  their  Properties  and  Treatment. 

limestone  employed  as  a  flux,  and  in  minute  quantity  in 
the  coal.  These  phosphates  contain  phosphorus  in  a  state 
of  combination  with  oxygen,  which  is  abstracted  by  the 
carbon  of  the  fuel  in  the  blast-furnace,  and  the  phosphorus 
thus  set  free  enters  into  combination  with  the  iron.  So 
completely  is  the  phosphorus  taken  up  by  the  metal,  that 
only  traces  of  that  element,  in  the  form  of  phosphates,  are 
usually  found  in  the  slag  from  the  blast-furnace.  The  effects 
of  phosphorus  are  to  harden  the  cast  iron  and  to  increase  its 
fusibility. 

Sulphur,  though  almost  invariably  contained  in  cast  iron, 
rarely  forms  as  much  as  ^th  of  its  weight.  It  may  be 
derived,  as  already  stated,  from  iron  pyrites  contained  in 
the  ore  or  in  the  coal,  or  even  from  sulphates  (of  lime,  for 
example)  contained  in  some  of  the  materials  forming  the 
charge;  for  the  oxygen,  with  which  the  sulphur  is  combined 
in  the  sulphates,  would  be  easily  removed,  and  the  sulphur 
would  combine  with  the  iron,  forming  a  sulphuret  of  iron 
which  is  dissolved  in  the  rest  of  the  metal.  The  white 
varieties  of  cast  iron  contain  a  larger  proportion  of  sulphur 
than  the  grey,  and  it  is  generally  admitted  that  the  presence 
of  sulphur  diminishes  the  strength  of  cast  iron  in  a  very  high 
degree. 

The  following  table  illustrates  the  general  composition  of 
the  three  principal  varieties  of  cast  iron : — 

Grey          Mottled         White 


Iron      .         .         .              90-24 

89-31 

89-86 

Combined  Carbon 

I  -02 

1-79 

2-46 

Graphite 

2-64 

i-ii 

0-87 

Silicon 

3-06 

2-17 

l'I2 

Sulphur 

1-14 

1-48 

2-52 

Phosphorus 

0-93 

ri-7 

O-gi 

Manganese 

0-83 

i  -60 

2-72 

99-86        98-63       100-46 


It  must  be  observed  that  the  difficulties  attending  the 
chemical  analysis  of  cast  iron  are  very  great,  on  account  of 


Varieties  of  Cast  Iron.  43 

the  large  quantity  of  iron  which  has  to  be  separated  from 
small  quantities  of  the  other  constituents,  so  that,  although 
numerous  analyses  are  recorded,  their  results  do  not  exhibit 
that  agreement  which  is  necessary  in  order  that  the  com 
position  of  this  material  may  be  considered  to  be  thoroughly 
established. 

The  average  tensile  strength  of  cast  iron  is  about  seven 
tons  per  square  inch. 

For  the  useful  applications  of  cast  iron,  eight  varieties  are 
commonly  recognised.  Nos.  i,  2  and  3  are  decidedly  grey 
irons,  of  different  shades,  i  being  the  greyest;  they  are  dis 
tinguished  by  the  sparkling  largely  crystalline  appearance 
of  the  broken  surface,  and  are  called  melting  iron  because 
they  are  chiefly  used  for  fine  castings.  No.  4  is  best  grey 
forge  iron,  and  No.  5,  grey  forge;  they  do  not  become  so 
liquid  when  melted  as  the  preceding,  but  they  are  tougher 
and  better  fitted  for  purposes  where  strength  is  required. 
No.  5  is  also  used  for  the  manufacture  of  wrought  iron,  as  is 
also  No.  6  or  strong  forge,  which  is  still  less  grey  in  quality. 
No.  7  is  a  decidedly  mottled  iron,  and  No.  8  is  white. 

A  less  elaborate  classification  is  generally  employed  among 
engineers ;  Nos.  i,  2  and  3  being  made  to  include  all  shades, 
from  dark  grey  (No.  i)  to  white  (No.  3). 

Grey  cast  iron  is  usually  regarded  as  the  proper  or  normal 
product  of  a  blast-furnace  in  good  working  order,  supplied 
with  a  due  proportion  of  fuel,  and  the  separation  of  the 
shining  scales  of  graphite  or  kish  upon  the  surface  of  the 
cast  is  commonly  looked  for  as  an  indication  of  the  satis 
factory  performance  of  the  furnace.  If  the  quantity  of  fuel 
employed  be  too  small  in  proportion  to  the  ore,  a  white  cast 
iron  is  produced,  and  a  larger  proportion  of  iron  is  found  in 
the  slag,  to  which  it  imparts  a  nearly  black  colour.  The 
slag  from  a  furnace  yielding  white  iron  frequently  contains 
about  5  per  cent,  of  the  metal,  whilst  the  slag  from  grey 
iron  seldom  contains  more  than  2  per  cent.  Slags  which 
contain  much  iron,  like  those  from  white  iron,  also  contain 


44        Metals :  their  Properties  and  Treatment. 

appreciable  quantities  of  phosphorus  in  the  form  of  phos 
phoric  acid. 

At  the  Dowlais  Foundry  the  capacity  of  the  furnaces  is 
275  cubic  yards.  When  grey  iron  is  manufactured,  these  are 
charged,  for  every  ton  of  iron  obtained,  with 

48  cwt.  Calcined  Ore  (Clay  Ironstone) 

50    ,,     Coal 

17    „     Limestone 

the  blast  being  supplied  at  the  rate  of  5,390  cubic  feet  per 
minute. 

When  white  forge  iron,  for  conversion  into  bar,  is  made, 
the  same  furnaces  are  charged,  for  every  ton  of  iron,  with 

28  cwt.  Calcined  Ore 

10    ,,     Haematite 

10    ,,     Slag  (Forge  and  Finery  Cinders) 

42    ,,     Coal 

14    ,,     Limestone 

the  blast  being  supplied  at  the  rate  of  7,370  feet  per  minute. 
In  this  case,  then,  one-sixth  less  coal  and  one-third  more  air 
are  employed  for  the  production  of  the  white  than  for  the 
grey  iron.  The  weekly  produce  of  the  furnace  is  170  tons 
when  white  iron  is  being  made,  and  only  130  tons  of  grey 
iron.  The  slag  is  about  twice  the  weight  of  the  metal. 
The  production  of  iron  in  winter  exceeds  that  in  summer  by 
four  or  five  per  cent,  because,  in  the  latter  season,  there  is 
more  vapour  of  water  in  the  blast,  which  lowers  the  tem 
perature  of  the  furnace. 

The  position  and  direction  of  the  tuyeres  materially  influ 
ence  the  character  of  the  pig  iron  obtained  in  the  crucible  ; 
when  forge  pig  is  being  made,  they  are  more  inclined  down 
wards  so  as  to  direct  the  blast  upon  the  metal  and  partially 
refine  it,  but  when  foundry  iron  is  the  desired  product,  they 
are  raised  higher  above  the  bottom  stone  of  the  furnace,  so 
that  the  blast  shall  not  oxidise  the  cast  iron  in  the  crucible. 
The  influence  of  a  large  relative  volume  of  slag  in  favouring 


Hot- Blast  Iron.  45 

the  production  of  grey  iron  also  depends  upon  its  shielding 
the  metal  from  the  oxidising  influence  of  the  blast. 

The  production  of  white  iron  when  the  supply  of  fuel  is 
deficient,  has  been  plausibly  referred  to  the  lower  tempera 
ture  of  the  furnace,  on  the  supposition  that  the  particular 
compound  of  carbon  with  iron,  which  is  present  in  white  iron, 
is  decomposed  by  a  higher  temperature  (when  more  fuel  is 
employed)  into  free  carbon,  which  separates  as  graphite  on 
cooling,  and  a  compound  of  iron  with  the  smaller  proportion 
of  carbon  which  exists  combined  in  grey  iron.  The  tendency 
of  manganese  to  favour  the  production  of  white  iron  may  be 
due  to  its  forming  a  compound  with  carbon  which  resists 
decomposition  at  a  high  temperature,  and  the  chemical 
similarity  existing  between  manganese  and  iron  favours  the 
belief  that  a  carbide  of  manganese  dissolved  in  iron  would 
produce  an  influence  similar  to  that  of  a  carbide  of  iron 
upon  the  properties  of  the  metal. 

It  sometimes  happens  that  grey  and  white  cast  iron  run 
from  the  crucible  of  the  furnace  at  the  same  tapping,  in  con 
sequence  of  some  variation  in  the  progress  of  the  smelting 
operation  during  the  interval  which  has  elapsed  since  the 
crucible  was  last  tapped.  Advantage  is  sometimes  taken  of 
this,  in  order  to  form  mottled  iron  for  casting  rollers,  by  first 
conducting  the  process  so  as  to  obtain  grey  iron,  and  then 
increasing  the  charges  of  ore,  decreasing  the  fuel,  and 
applying  a  higher  pressure  of  blast,  so  as  to  produce  a  white 
iron. 

The  belief  is  very  common  that  iron  smelted  with  the  hot 
blast  is  inferior  in  quality  to  that  obtained  from  a  cold-blast 
furnace,  though  it  does  not  clearly  appear  to  have  been 
proved  that,  all  other  conditions  being  the  same,  the  tempe 
rature  of  the  blast  does  make  a  difference  in  the  quality 
of  the  cast  iron  obtained.  The  smaller  quantity  of  fuel 
employed  in  a  hot-blast  furnace  might  be  the  cause  of  the 
alleged  inferiority  of  the  iron.  The  higher  temperature  in 
the  hearth  of  the  hot-blast  furnace  also  facilitates  the  forma- 


46        Metals :  their  Properties  and  Treatment. 

tion  of  a  pig  iron  rich  in  silicon.  Moreover,  part  of  the 
charge  introduced  into  a  hot- blast  furnace  often  consists  of 
slag  or  cinder  formed  during  the  process  of  puddling  the 
cast  iron  in  order  to  convert  it  into  bar  iron.  This  cinder 
contains  more  than  half  its  weight  of  iron  which  it  is  desired 
to  recover,  but  it  also  contains  a  large  proportion  of  phos 
phorus  and  sulphur,  by  which  the  quality  of  the  cast  iron  is 
deteriorated.  It  is  not  uncommon  to  employ  a  mixture  of 
ore  with  ^th  of  this  cinder  in  a  hot-blast  furnace,  and  the 
cinder  iron  so  obtained  is  inferior  in  quality  and  lower  in 
price  than  the  mine  iron,  which  is  smelted  from  ore  only. 
The  temperature  prevailing  in  a  cold-blast  furnace  is  not 
usually  adequate  to  the  smelting  of  such  slags,  so  that  cold- 
blast  iron  is  not  so  liable  to  impurities  from  this  source. 

Some  of  the  latest  experiments  upon  the  comparative 
strengths  of  hot-blast  and  cold-blast  irons  appear  to  warrant 
the  conclusion  that  so  far  as  the  temperature  of  the  blast 
only  is  concerned,  the  hot-blast  tends  slightly  to  injure  the 
quality  of  the  softer  (grey)  irons,  whilst  it  improves,  sometimes 
in  a  very  marked  degree,  the  character  of  the  harder  (white) 
cast  irons. 

Remelting  of  Cast  Iron  in  the  Foundry. — In  order  to  melt 
the  pig  iron  for  the  production  of  castings,  a  cupola  furnace 
is  employed.  The  construction  of  this  furnace  varies  in 
different  foundries,  but  it  is  now  commonly  made  of  the 
form  represented  in  Fig.  9,  being  cased  with  thick  iron 
plates  strongly  riveted  together,  and  protected  internally  by  a 
layer  of  binding  sand  about  nine  inches  thick.  At  different 
heights  up  the  sides  of  the  furnace  there  are  openings  G  for 
the  introduction  of  blast-pipes,  two  or  three  of  which  are 
employed  at  one  time,  the  remaining  openings  being  closed 
by  iron  doors.  For  melting  5  tons  of  cast  iron,  the 
cupola  furnace  is  9  feet  high,  and  3^  feet  in  diameter,  clear 
of  the  lining.  The  tuyere  holes,  6  inches  in  diameter, 
are  placed  at  intervals  of  15  inches,  the  lowest  being  30 
inches  from  the  bottom,  which  is  made  to  slope  a  little 


Remelting  of  Cast  Iron. 


47 


towards  the  gutter  E  by  which  the  melted  iron  is  run  out. 
A  conical  iron  hood  D  surmounts  the  furnace,  connecting  it 
with  the  chimney,  and  having  an  opening  for  introducing 
the  metal  and  fuel.  A  wood  fire  is  first  lighted  in  the 
cupola,  through  the  tap-hole,  and  a  quantity  of  coke  having 
been  thrown  in,  and  well  ignited  by  the  blast,  the  tap-hole  is 
closed,  and  the  pig  iron  introduced  in  pieces  of  about  28  Ibs. 
each,  together  with  one-fourth  of  its  weight  of  coke.  Fresh 
charges  are  introduced  about  every  quarter  of  an  hour,  until 
the  whole  of  the  iron 
is  melted,  when  the 
tap-hole  is  unstopped 
and  the  metal  run, 
either  into  moulds 
sunk  into  the  floor 
upon  which  the  fur 
nace  stands,  or  into  a 
casting-ladle,  whence 
it  is  transferred  to  the 
moulds. 

During  the  process 
of  remelting,  about 
five  or  six  parts  of 
iron  out  of  a  hundred 
are  wasted  by  com 
bining  with  the  oxy 
gen  of  the  air  to  form 
an  oxide  of  iron, 
which  unites  with 

silica  from  the  lining  of  the  furnace  to  form  a  slag.  The 
quality  of  the  iron  is  generally  improved  in  the  process  in 
consequence  of  the  refining  influence  of  the  air,  and  a  highly 
carburetted  iron  is  employed,  lest  the  fusibility  of  the  cast 
iron  should  be  diminished  in  consequence  of  the  reduction 
in  the  proportion  of  carbon.  It  is  necessary  to  employ  coke 
as  free  from  sulphur  as  possible,  and  a  small  quantity  of 


FIG.  9.— Front  and  Back  Views  of  Cupola  Fur 
nace.  A,  Foundation  of  Masonry  covered 
with  Iron  Plates  B. 


48         Metals:  their  Properties  and  Treatment. 

lime  is  not  imfrequently  introduced  with  the  iron,  in  order  to 
combine  with  the  silica  contained  in  the  coke,  and  prevent 
excessive  waste  of  iron  in  the  slag ;  but  the  lime  is  liable  to 
corrode  the  lining  of  the  furnace. 

When  casting  in  sand,  it  is  necessary  to  prevent  the  direct 
contact  of  the  melted  metal  with  the  sand,  lest  it  should  be 
chilled ;  for  this  purpose  the  iron-moulder's  blacking  is  used, 
which  is  generally  charred  oak-wood  ground  to  powder  ; 
the  gas  evolved  by  this  under  the  action  of  the  heated  iron 
suffices  to  prevent  the  conta.ct  of  the  metal  with  the  mould. 

For  some  purposes  it  is  found  advantageous  to  melt  the 
foundry  iron  with  about  one-third  of  scrap  wrought  iron. 

In  order  to  protect  castings  from  rust,  they  are  brushed 
over  with  linseed  oil,  and  suspended  over  a  very  smoky 
wood  fire,  being  afterwards  dipped  into  turpentine,  when 
they  acquire  a  bright  carbonaceous  protective  coating. 

The  following  table  shows  the  proportions  of  materials 
employed,  to  yield  one  ton  of  cast  iron,  in  some  of  the  most 
important  British  iron  districts : — 

Staffordshire  Yorkshire  Scotland  South  Wales 

Ore  .   40  to  60  cwt.  70  cwt.  36  cwt.  (calcined)      67  cwt. 

Limestone   15  to  18    ,,  20    ,,  10    ,,  17    ,, 

Coal         .60  „  80    ,,  30    „  35  to  37    „ 

The  iron  made  in  Staffordshire  is  chiefly  forge  iron  for  con 
version  into  common-  bar  iron ;  Yorkshire  produces  forge 
iron  for  making  best  bar  and  plate  ;  Scotland  furnishes 
foundry  iron ;  and  Wales  forge  iron  for  conversion  into  rail 
way  bar  iron. 

CONVERSION   OF   CAST    IRON    INTO   WROUGHT   OR    BAR 
IRON. 

To  obtain  iron  in  a  state  fit  for  rolling  into  strong  bars, 
boiler  plates,  &c.,  it  is  necessary  to  deprive  the  cast  iron  as 
far  as  possible  of  all  foreign  matters,  except  a  small  propor 
tion  of  carbon,  of  which  a  quantity  not  exceeding  ^^-th  is 
found  to  increase  the  toughness  of  the  iron. 


Refining  of  Cast  Iron.  49 

The  chemical  agent  employed  to  effect  the  purification  of 
the  iron  is  oxygen,  which  is  supplied  by  atmospheric  air. 

When  iron  is  heated  to  redness  in  air,  it  combines  with 
oxygen  and  becomes  coated  with  black  oxide  of  iron,  which 
is  detached  in  scales  when  the  iron  is  struck  with  a  hammer, 
and  is  more  easily  melted  than  iron.  If  iron  containing 
carbon  be  strongly  heated  in  contact  with  the  black  oxide  of 
iron,  the  latter  parts  with  its  oxygen  to  the  carbon,  which  it 
converts  into  carbonic  oxide  gas.  If  silicon  be  present  in 
the  iron,  it  combines  with  the  oxygen  to  form  silica ;  this 
unites  with  another  portion  of  oxide  of  iron,  yielding  a  silicate 
of  iron  which  becomes  liquid  at  a  high  temperature,  forming 
a  slag  easily  separated  from  the  purified  iron.  Manganese 
combines  with  oxygen  even  more  readily  than  iron,  forming 
an  oxide  of  manganese  which  is  easily  dissolved  in  the  liquid 
slag. 

The  most  important  of  the  processes  employed  for  the 
conversion  of  cast  iron  is  that  of  puddling,  but  this  was  for 
merly  often  preceded  by  a  refining  process  which  will  there 
fore  be  first  described,  although  it  is  now  comparatively 
seldom  employed. 

The  finery  furnace  or  running  out  fire  (Fig.  10),  in  which 
the  process  of  refining  cast  iron  is  carried  on,  is  an  oblong 
trough  (A)  made  of  cast  iron,  three  sides  of  which  are 
enclosed  by  double  walls  (u)  which  are  kept  cool  by  water 
circulating  between  them;  it  is  about  3  feet  long,  2  feet 
wide,  and  2 \  feet  deep,  the  floor  being  rammed  with  sand 
and  made  somewhat  concave.  This  trough  is  furnished  with 
two,  four  or  even  six  blast-pipes  (/),  similar  in  construction 
to  those  of  the  blast  furnace,  and  inclined  at  an  angle  of 
twenty  or  thirty  degrees  to  the  floor  of  the  hearth,  so  that 
the  blast  may  be  directed  on  to  the  metal.  About  400  cubic 
feet  of 'air  per  minute  are  usually  supplied  to  the  finery, 
giving  a  pressure  of  about  3  Ibs.  per  inch.  The  hearth  of 
the  furnace  having  been  filled  with  coke,  four  pigs  of  iron 
are  arranged  upon  it,  parallel  to  the  four  sides  of  the  hearth, 

E 


50         Metals :  their  Properties  and  Treatment. 

and  two  more  are  placed  transversely  over  them ;  coke  is 
heaped  up  over  the  pigs,  and  blown  into  a  strong  fire,  when 
the  cast  iron  gradually  melts,  and  is  partly  converted  into 


FIG.  10. — Hearth  for  refining  Cast  Iron,  in  section  and  plan.  A,  Hearth  in 
which  the  fuel  and  pig-iron  are  placed.  B,  Hollow  iron  supports  for  the 
chimney  c,  which  is  about  18  feet  high.  D,  Flat  mould  for  the  refined 
iron,  e,  Funnel-pipes  for  conveying  water  to  the  tuyeres,  i,  Pipes  for 
carrying  off  the  heated  water  from  the  tuyeres.  /,  Pipes  for  carrying  off 
the  heated  water  from  the  hollow  walls  u.  o,  Tap-hole  for  running  out 
the  fine  metal.  r,  Stopcocks  for  supplying  water  to  the  cisterns  v. 
s,  Valves  for  regulating  the  blast  issuing  from  the  pipes  T. 


Refined  Iron  or  Fine  MctaL  5 1 

oxide  by  the  blast  of  air ;  the  oxide  of  iron  imparts  oxygen 
to  the  silicon  present  in  the  cast  iron,  and  converts  it  into 
silica  which  combines  with  more  oxide  of  iron  to  form  the 
slag  or  finery  cinder.  The  coke  is  replaced  as  it  burns  away, 
so  that  four  or  five  hundredweight  are  used  for  refining  a  ton 
of  pig  iron.  In  about  two  hours,  the  tap-hole  (o)  is  opened, 
and  \hefine  metal  or  plate  metal  allowed  to  run  into  a  shallow 
cast-iron  mould  (D),  lined  with  loam  and  kept  cool  by  the 
circulation  of  water  beneath  it.  The  metal  is  thus  cast  into 
a  plate  about  ten  feet  long,  three  feet  wide  and  two  inches 
thick,  whilst  the  bulk  of  the  slag  runs  off  into  a  separate 
mould  beyond,  some  being  left  upon  the  surface  of  the  fine 
metal.  The  latter  is  chilled  by  throwing  water  upon  it, 
when  it  becomes  very  brittle,  and  is  easily  broken  into 
masses  fit  for  the  puddling  furnace. 

The  fine  metal,  as  might  be  expected  after  the  chilling, 
has  much  the  character  of  white  cast  iron,  but  it  has  been 
purified  from  the  greater  part  of  its  silicon,  and  the  propor 
tions  of  carbon,  manganese,  sulphur  and  phosphorus  have 
been  diminished.  The  phosphorus  combines  with  oxygen 
to  form  phosphoric,  acid  which  is  found  in  the  slag  as  phos 
phate  of  iron.  The  sulphur  passes  into  the  slag  as  sulphuret 
of  iron.  When  the  refined  iron  is  intended  for  the  manu 
facture  of  the  sheet  iron  with  which  tin  plate  is  made,  char 
coal  is  employed  in  the  refinery  instead  of  coke  which 
imparts  sulphur  to  the  metal,  but  the  charcoal  fire  does  not 
run  the  metal,  which  accumulates  in  soft  masses ;  these  are 
taken  out  and  hammered  into  flat  plates.  100  parts  of  pig 
iron  yield  only  from  85  to  90  parts  of  refined  iron,  the  loss 
representing  the  impurities  which  have  been  removed,  and 
that  portion  of  the  iron  which  has  been  carried  into  the  slag 
in  the  form  of  oxide. 

One  finery  hearth  is  capable  of  refining  ten  tons  of  cast 
iron  in  twenty-four  hours,  so  that  it  is  able  to  keep  pace  with 
the  blast-furnace. 


E  2 


5  2        Metals :  their  Properties  and  Treatment. 

In  some  works  the  pig  iron  is  run  into  the  finery  hearth 
direct  from  the  blast-furnace. 

The  slag  from  the  refining  process,  or  finery  cinder,  consists 
essentially  of  silicate  of  iron,  composed,  in  100  parts,  of  about 
69  parts  of  oxide  of  iron  (protoxide  of  iron  or  ferrous  oxide) 
and  3 1  parts  of  silica,  but  it  always  contains  sulphuret  of  iron 
and  phosphate  of  iron,  as  well  as  manganese,  magnesium 
and  other  metals  in  small  quantity,  which  were  present  in 
the  cast  iron.  As  the  31  parts  of  silica  contain  14^  parts  of 
silicon,  and  the  69  parts  of  oxide  of  iron  contain  53^  parts  of 
metallic  iron,  it  is  evident  that  the  silicon  contained  in  the 
pig  iron  involves  a  loss  of  nearly  four  times  its  weight  of  iron 
in  the  slag. 

The  Puddling  Process. — This  process  depends  upon  the 
same  chemical  principles  as  the  refining  just  described,  but 
differs  widely  from  it  in  the  mode  of  manipulation,  the 
object  of  the  puddler  being  to  stir  up  together  the  melted 
or  softened  iron  with  melted  oxide  of  iron,  so  as  to  ensure 
the  contact  of  the  latter  with  every  portion  of  the  metal  upon 
which  its  purifying  influence  is  to  be  exerted. 

The  furnace  in  which  the  puddling  is  executed  is  of  the 
kind  known  as  reverberator y*  so  named  from  its  having  an 
arch  which  beats  back  the  flame  on  to  the  iron  to  be 
heated. 

This  furnace  is  represented  in  Fig.  n,  being  built  of  fire 
brick,  and  either  tightly  bound  with  iron  bars,  or  even 
entirely  cased  with  cast-iron  plates,  since  it  is  required  to 
maintain  a  very  high  temperature  in  the  furnace,  which 
would  crack  the  brick-work  unless  it  was  well  secured. 

The  grate  F  of  this  furnace  is  of  unusually  large  dimen 
sions,  measuring  about  4  feet  by  3,  so  that  the  coal,  which  is 
the  fuel  employed,  may  give  a  large  volume  of  flame  to  be 
drawn  through  the  furnace  by  the  draught  of  the  chimney  (c) 
and  forced  by  the  arch  to  play  upon  the  metal  on  the  hearth 
(A)  before  it  escapes  through  the  flue. 

*  From  the  Latin  reverbero,  to  beat  back. 


The  Puddling  Furnace. 


53 


The  hearth  (A)  is  generally  about  6  feet  in  length  and  4  feet 
across  the  widest  part  opposite  to  the  working-door  (D.)  Its 
construction  varies  much  in  different  places,  but  it  is 
generally  made  of  cast-iron  plates,  supported  upon  cast-iron 
pillars,  so  that  they  may  be  kept  below  the  melting  point  by 
the  exposure  of  their  under  surfaces  to  the  air.  In  order  to 


FIG.  ii. — Puddling  Furnace. 

prevent  these  plates  from  being  rapidly  corroded,  they  are 
commonly  protected  by  a  coating  of  slag.  At  the  end  of  the 
hearth  nearest  to  the  grate,  is  a  fire-bridge  of  brick,  which 
prevents  the  coal  from  coming  into  contact  with  the  metal 
on  the  hearth,  and  at  the  other  end,  near  the  chimney,  a 
brick  ledge,  or  altar,  about  2\  inches  high,  prevents  the  iron 


54         Metals:  tJieir  Properties  and  Treatment. 

from  running,  out  of  the  hearth.  At  this  part,  the  width  of 
the  hearth  is  2  feet.  The  height  from  the  hearth  to  the 
highest  part  of  the  arch  is  2  feet,  but  towards  the  chimney 
it  is  only  8  inches. 

Beyond  the  altar  is  an  inclined  plane  of  fire-brick  (B),  down 
which  the  slag  runs,  being  discharged  from  the  furnace 
through  \h&  floss-lwle  (/*),  near  which  a  small  fire  is  maintained 
outside  the  furnace,  to  prevent  the  slag  from  solidifying. 

The  chimney  varies  from  30  to  50  feet  in  height,  and  is 
provided  with  an  iron  plate  attached  to  a  lever  by  which  it 
may  be  raised  or  lowered  at  the  will  of  the  puddler.  so  as  to 
increase  or  diminish  the  draught  through  the  furnace. 

The  main  working-door  of  the  furnace,  situated  at  the 
widest  part  of  the  hearth,  is  closed  by  an  iron  door  suspended 
from  a  lever  with  a  counterweight,  so  that  it  may  be  readily 
raised  or  lowered.  In  this  door  there  is  an  opening  about 
5  inches  square,  through  which  the  puddler  thrusts  the  rake, 
paddle  or  rabble,  with  which  the  iron  is  stirred.  Immediately 
beneath  this  door  is  another  floss-hole  stopped  with  loam, 
which  can  be  opened  at  pleasure  for  the  discharge  of  slag. 
Larger  furnaces  with  two  doors,  enabling  two  puddlers  to 
work  at  opposite  sides,  are  now  often  employed. 

The  charging-door  through  which  the  metal  to  be  puddled 
is  introduced  is  situated  at  the  cooler  part  of  the  hearth, 
near  the  chimney.  The  charge  of  a  puddling-furnace  con 
sists  of  only  4  or  5  cwt.  of  pig  iron  or  refined  iron  (usually 
mixed  with  grey  pig  iron),  which  is  broken  into  fragments,  and 
piled  in  heaps  around  the  sides  of  the  furnace.  It  is  usual, 
especially  when  unrefined  pig  iron  is  being  puddled,  to  add 
a  quantity  of  hammer-slag  or  iron  scales  (black  oxide  of 
iron)  in  the  proportion  of  about  one-fifth  of  the  weight  of  the 
metal,  so  as  to  obviate  the  necessity  for  allowing  so  large  a 
quantity  of  the  latter  to  combine  with  the  oxygen  of  the  air 
in  order  to  form  sufficient  oxide  to  effect  the  purification  of 
the  metal.  Even  red  haematite  is  sometimes  added  with  the 
same  object. 


The  Puddling  Process,  5  5 

The  charging  door  is  now  closed  with  an  iron  plate,  and 
the  grate  is  filled  with  coal,  which  is  heaped  up  so  as  to 
close  the  fire-door  completely.     The  damper  at  the  top  of 
the  chimney  being  fully  opened,  so  as  to  create  a  strong 
draught,  the  metal  upon  the  hearth  is  soon  brought  to  a 
high  temperature,  and  in  about  twenty  minutes  it  begins  to 
melt.     If  it  were  allowed  to  become  very  rapidly  liquid,  the 
iron  would  be  oxidised  only  to  a  slight  extent  upon  the  surface, 
and  the  object  of  the  puddling  process  would  be  defeated  ; 
accordingly,  a  workman  rakes  the  melting  fragments  into  a 
cooler  part  of  the  hearth,  and  exposes  fresh  surfaces  of  the 
metal  to  the  oxygen  of  the  air  in  the  furnace.     In  about  ten 
minutes  more,  the  whole  of  the  metal  has  become  fused  to  a 
pasty  condition,  and  the  skill  of  the  puddler  is  now  brought 
into  play,  to  mix  the  semi-fluid  metal  with  the  melted  oxide 
of  iron  upon  its  surface,  by  stirring  it  with  a  paddle  intro 
duced  through  the  hole  in  the  working  door.     At  this  stage 
much  depends  upon  the  consistence  of  the  metal,  which  may 
be  modified  by  judicious  regulation  of  its  temperature,  for  it 
is  obvious  that  if  the  metal  were  in  a  perfectly  thin  and 
liquid  condition,  it  could  not  be  well  incorporated  with  the 
oxide  which  is  to  purify  it ;   the  puddler  therefore  lowers 
the  fire,  partially  closes  the  damper,  and  sometimes  chills 
the  metal  by  throwing  water  upon  it.     As  the  stirring  or 
puddling  is  proceeded  with,  the  metal  froths  or  swells  up 
very   much,   and   evolves   numerous   bubbles   of    carbonic 
oxide   gas,   indicating  the  progress  of  the  removal  of  the 
carbon    from    the    iron.      When    unrefined    pig    iron    is 
puddled,  this  boiling  of  the  metal  is  more  marked  than  in 
the  case  of  refined  iron,  because  the  metal  is  more  liquid, 
and  hence    the    puddling    of    refined    iron    is   sometimes 
distinguished  as  dry  puddling,  that  of  raw  iron  being  called 
pig  boiling.     In  a  short  time   small   clotted   lumps  of  the 
purified  iron  separate  or  come  to  nature  in  the  melted  metal, 
the  temperature  of  which  is  not  high  enough  to  fuse  the  iron 
when  nearly  deprived  of  its  carbon,  and  at  the  end  of  an 


56        Metals :  their  Properties  and  Treatment. 

hour,  so  much  purified  iron  has  thus  been  separated  that  the 
charge  works  dry  or  sandy,  and  by  this  time  the  disengage 
ment  of  carbonic  oxide  has  almost  ceased.  It  is  now 
requisite  to  raise  the  temperature  so  as  to  soften  the  particles 
of  purified  iron,  and  allow  of  their  being  welded  into  a 
compact  mass.  With  this  view,  the  fire  is  made  up,  and  the 
damper  gradually  raised  until  the  particles  of  iron  are  so  far 
softened  that  they  stick  together  and  cause  the  mass  to  work 
heavy  under  the  paddle.  A  little  of  the  soft  metal  is  now 
collected  upon  the  end  of  the  paddle,  and  rolled  about  upon 
the  hearth  until  a  ball  or  bloom  of  about  60  Ibs.  weight  has 
been  collected  ;  this  is  placed  in  the  hottest  part  of  the 
hearth,  near  the  bridge,  so  as  thoroughly  to  soften  the 
metallic  particles,  which  are  then  pressed  together  with  the 
paddle  in  order  to  squeeze  the  slag  from  between  them  and 
to  render  the  mass  more  compact.  When  the  whole  of  the 
metal  has  been  thus  made  up  into  (five  or  six)  balls,  the 
opening  in  the  working  door  is  stopped  with  a  brick,  and 
the  temperature  is  raised  to  a  full  welding  heat.  Each  ball 
is  then  lifted  out  of  the  furnace  on  the  end  of  an  iron  rod  or 
porter  which  is  pressed  into  it,  and  placed  under  a  hammer 
capable  of  delivering  about  a  hundred  powerful  blows  in  a 
minute,  the  ball  being  turned  about  under  it,  by  the  iron  rod 
which  serves  as  a  handle,  when  the  melted  slag  is  forced  out, 
in  white  hot  showers,  from  between  the  particles  of  iron,  and 
these  become  welded  together  into  a  stamping,  or  compact 
mass  of  metal  of  an  oblong  form  which  is  rolled  out  into 
bars  between  the  puddling  rolls.  These  consist  of  a  pair  of 
massive  iron  cylinders  (A  A',  Fig.  12),  the  surfaces  of  which 
are  so  grooved  that  when  the  cylinders  are  placed  together 
they  exhibit  a  series  of  gradually  diminishing  openings,  the 
first  few  being  nearly  oval,  and  the  remainder  (B  B7)  capable 
of  rolling  flat  bars.  The  first  two  or  three  grooves  are 
notched  like  files  so  that  they  may  readily  take  hold  of  the 
metal  presented  to  them,  which  is  passed  backwards  and 
forwards  by  workmen  stationed  on  opposite  sides  of  the 


Rolling  the  Puddled  Iron. 


57 


rolls,  being  sent  through 
the  first  groove  five  or  six 
times.  These  rolls,  being 
made  to  revolve  in  opposite 
directions,  powerfully  com 
press  the  metal,  and  squeeze 
out  any  remaining  slag. 
The  bar  is  so  turned  about 
before  being  passed  through 
each  of  the  elliptical  open 
ings,  that  the  pressure  may 
be  equally  applied  to  all 
sides  of  it.  So  dexterous 
are  the  workmen  employed 
in  the  rolling,  that  a  minute 
and  a  half  will  often  suffice 
for  the  conversion  of  the 
rough  metal  into  a  flattened 
bar,  which  is  generally  4 
inches  wide,  J  to  i  inch 
thick,  and  10  or  12  feet 
long. 

The  rolls  are  generally 
cast  in  chill  (p.  39),  but  so 
that  the  chill  may  not  pene 
trate  too  deep  and  render 
the  rolls  brittle. 

For  producing  bars  of 
any  special  pattern,  such 
as  railway  bars,  rollers  are 
employed  which  have 
grooves  capable  of  impart 
ing  the  required  form  to 
the  bar  passed  between 
them.  During  the  rolling 
of  the  bars,  they  are  main- 


5  8        Metals :  their  Properties  and  Treatment. 

tained  at  a  sufficiently  high  temperature  by  the  latent  heat 
which  is  extricated  in  consequence  of  the  compression  of  the 
particles  of  metal.  It  is  often  necessary  to  allow  a  small 
stream  of  water  to  trickle  over  the  rolls  in  order  to  prevent 
them  from  becoming  over-heated  and  sticking  to  the  metal. 
In  some  ironworks,  the  compression  of  the  puddled  balls 
is  effected  between  the  jaws  of  a  powerful  squeezer  (Fig.  13) 
worked  by  steam  power,  but  a  ponderous  Nasmyth's  steam 
hammer  is  now  commonly  employed,  its  invention  having 
very  materially  assisted  to  develop  and  improve  the  art 
of  forging  iron.  In  others  the  puddled  balls  are  carried  at 
once,  by  tongs,  to  the  bloom-squeezers  (Fig.  14),  a  succession 


FIG.  13.— Squeezer  for  Puddled  Balls. 

of  three  pairs  of  heavy  rollers,  of  which  the  upper  pair  are 
grooved  longitudinally  to  bite  the  bloom.  On  issuing  from 
these  the  compressed  bloom  is  caught  by  a  projection 
attached  to  an  endless  chain  by  which  it  is  lifted  up  to 
the  platform  in  front  of  the  roughing-rolls,  when  it  is  seized 
by  the  workman  and  forced  into  the  largest  groove. 

Another  machine  for  compressing  the  blooms  consists  of 
a  massive  iron  table  (B,  Fig.  1 5)  with  a  strong  elliptical  ledge 
(E),  within  which  an  iron  cylinder  (c)  is  made  to  revolve,  so 
that  a  much  wider  interval  (A)  is  left  between  its  circumfer 
ence  and  the  ledge  at  one  end  than  at  the  other ;  the  bloom 
(D)  being  placed  at  the  wider  end,  is  carried  round  as  the 
cylinder  revolves,  being  well  squeezed  in  its  progress,  and 


Squeezing  the  Blooms. 


59 


60        Metals  :  their  Properties  and  Treatment. 

delivered  from  the  narrow  end  fit  for  passing  through  the 
rolls. 

The  process  of  puddling  occupies  about  two  hours,  so 
that  it  is  necessary  to  provide  five  puddling  furnaces  in 
order  to  work  up  the  iron  furnished  by  one  blast-furnace 
and  one  refinery.  The  coal  consumed  is  about  equal  in 
weight  to  the  metal  puddled. 

From  90  to  92  parts  of  puddled  bars  are  made  from  100 
parts  of  fine  metal  by  a  skilled  puddler,  but  when  the  pro 
cess  is  badly  managed,  a  larger  proportion  of  the  iron  is 
oxidised  and  carried  off  in  the  slag. 

The  slag  or  tap-cinder  from  the  puddling  furnace  is  often 
termed  by  chemists  a  highly  basic 
silicate  of  iron,  for  it  contains  a 
very  large  proportion  of  oxide 
of  iron  and  a  small  proportion 
of  silica,  but  it  always  contains 
much  phosphorus  and  sulphur 
extracted  from  the  iron,  these 
being  present,  respectively,  in 
the  forms  of  phosphate  and  sul- 
phuret  of  iron.  The  results  of 
FIG.  15.—  Cylindrical  Rotating  the  analysis  of  a  sample  are 

Squeezer  for   Puddled   Balls,  ,  .     . 

seen  from  above.  Subj  Oined. 

Composition  of  Tap-  Cinder  from  Puddling  furnace. 

/Iron  .......  54'33 

\Oxygen  ......  16-87 

Silica  .......       8-32 

.,  f  Phosphorus  .  .  3-  1  8 

Phosphoric  acid  |  •         • 


rr        f  Sulphur.          .         .       2-57 
Sulphuretoflron|lro£       .         .         .       4-50 

Lime  .......       47° 

Oxide  of  Manganese     .         .         .         .078 

Magnesia     ......       0-26 


The  lime  in  this  sample  is  due  to  the  employment  of  that 


Composition  of  Puddled  Bar.  61 

substance  as  a  lining  for  the  hearth  of  the  puddling  furnace 
in  order  to  assist  in  the  removal  of  the  sulphur. 

It  is  evident  that  the  waste  of  iron  in  the  process  of  pud 
dling  will  be  greater  in  proportion  as  the  crude  metal  is 
richer  in  silicon,  since  this  element  requires  at  least  four 
times  its  weight  of  iron  to  be  added  in  the  form  of  oxide,  in 
order  to  convert  it  into  a  fusible  slag. 

It  has  been  observed  that  when  the  slag  contains  much 
manganese,  the  removal  of  the  phosphorus  and  sulphur  from 
bar  iron  is  more  complete,  though  the  puddling  is  then 
attended  with  more  difficulty.  The  phosphorus  appears 
then  to  be  converted  into  phosphate  of  manganese,  from 
which  the  phosphorus  cannot  be  again  reduced  and  restored 
to  the  iron,  as  is  the  case  when  it  is  converted  into  phos 
phate  of  iron.  The  removal  of  the  sulphur  seems  to  be 
facilitated  by  the  circumstance  that  the  silicate  of  manganese 
formed  in  the  slag  has  the  property  of  dissolving  the  sul- 
phuret  of  iron  at  a  high  temperature. 

The  extent  to  which  the  most  important  foreign  sub 
stances  are  removed  from  the  pig  iron  by  puddling,  may  be 
inferred  from  the  following  comparison  of  the  composition 
of  a  puddled  bar  with  that  of  the  good  No.  3  grey  cold-blast 
Staffordshire  pig  from  which  it  was  obtained  : — 


Pig  Iron  Puddled  Bar 
Carbon      .                                    2-28  0-30 

272  O'I2 

0-65  0-14 


0-30  0-13 

94-05 


Silicon 
Phosphorus 
Sulphur     . 
Iron  . 

Although,  as  a  chemical  operation,  the  puddling  process 
may  be  regarded  as  effecting  a  very  difficult  purification  by 
very  simple  means, -as  a  manufacturing  process  it  does  not 
appear  in  so  favourable  a  light.  It  demands  from  the 
puddler  not  only  skilled  labour,  but  labour  of  the  most  ex 
hausting  description,  -which  .  must  be  rewarded  by  wages 
proportionally  high.  Exposed  half  naked  to  the  heat  of  the 


62         Metals :  their  Properties  and  Treatment. 

furnace,  and  nearly  blinded  by  its  glare,  the  endurance' of 
the  puddler,  is  tried  to  the  utmost,  and  attacked  very  fre 
quently  by  cataract  and  by  pulmonary  disease,  he  seldom 
lives  beyond  fifty,  an  age  at  which  men  labouring  under 
happier  conditions  scarcely  begin  to  show  signs  of  decay. 
Nor  does  the  expense  of  the  process  consist  only  in  high 
wages,  for  the  wear  and  tear  of  the  furnaces,  caused  by  the 
frequent  repetition  of  such  heavy  work,  is  attended  with  a 
great  outlay.  The  character  of  the  malleable  iron  obtained, 
in  so  far  as  it  depends  upon  the  proportion  of  carbon  re 
maining,  is  also  very  variable,  from  the  want  of  any  certain 
criterion  by  which  the  puddler  may  know  when  the  process 
should  be  discontinued.  A  great  many  processes  have  been 
devised,  from  time  to  time,  in  order  to  dispense  with  the 
puddling  operation  in  its  present  form.  Revolving  furnaces 
and  other  mechanical  arrangements  have  been  proposed,  to 
replace  the  manual  labour ;  steam  and  air  have  been  forced 
through  the  melted  pig  iron  in  various  ways,  to  facilitate  the 
chemical  changes  by  which  the  impurities  are  removed, 
but  the  only  process  which  has  been  attended  by  a  suffi 
cient  measure  of  success  to  attract  the  general  attention  of 
ironmasters  is  that  of  Bessemer,  which  consists  in  blowing 
air  through  the  melted  metal  in  a  huge  crucible,  so  that  the 
mechanical  agitation  caused  by  the  blast  may  exert  the  same 
beneficial  influence  as  the  labour  of  the  puddler.  Since, 
however,  this  treatment  does  not  effect  the  removal  of  the 
sulphur  and  phosphorus  from  the  metal,  it  is  not  able  to 
produce  good  bar  iron  from  any  but  the  best  qualities  of  pig, 
such  as  are  considered  too  expensive  for  conversion  into 
bar.  Its  application  in  this  country  is  therefore  in  great 
measure  limited  to  the  manufacture  of  Bessemer  steel,  and  a 
description  of  the  process  will  be  given  under  the  head  of 
Steel. 

In  Sweden  and  India,  where  charcoal  pig  iron  may  be 
obtained  at  a  cheaper  rate,  the  process  of  Bessemer  is 
extensively  adopted,  and  although  it  is  not  carried  out  in 


Characters  of  Puddled  Bar.  63 

precisely  the  form  of  apparatus  described  under  Steel,  there 
is  no  difference  in  the  principle. 

In  Silesia  the  conversion  of  the  cast  iron  into  malleable 
iron  is  effected  in  a  reverberatory  furnace  heated  by  the 
flame  of  a  mixture  of  coal  gas  and  air  which  are  supplied 
to  the  furnace  through  two  sets  of  tuyeres.  When  the  cast 
iron  is  melted  on  the  hearth  of  the  furnace,  a  little  limestone 
is  thrown  in,  and  two  strong  blasts  of  air  are  directed  upon 
the  surface  of  the  metal  from  separate  tuyeres,  introduced 
through  openings  on  each  side  of  the  hearth.  The  blast 
keeps  the  metal  in  constant  motion,  and  blows  away  the 
slag  from  the  surface  so  as  continually  to  expose  the  metal, 
which  is  also  occasionally  stirred  with  a  rake,  a  little  lime 
stone  being  occasionally  added.  Two  tons  of  pig  iron  are 
treated  in  this  furnace,  and  require  from  z\  to  5  hours. 
The  temperature  in  this  furnace  being  much  higher  than 
that  of  the  English  puddling-furnace,  the  iron  is  run  out  in  a 
perfectly  liquid  condition. 

The  ingots  or  bars  cast  from  the  melted  malleable  iron, 
whether  obtained  by  this  process  or  by  that  of  Bessemer, 
require  to  be  hammered  and  rolled  in  order  to  give  them 
the  usual  strength  of  bar  iron.  Thus,  a  given  specimen 
which  was  broken  by  a  tension  of  18^  tons  upon  the  square 
inch  when  first  cast  into  an  ingot,  required  a  tension  of  32^ 
tons  after  being  hammered  and  rolled. 

Conversion  of  Puddled  Bar  Iron  into  Merchant  and  Best 
Bar. — The  Mill  Bar  or  Puddled  Bar  Iron  obtained,  as 
described  above,  by  rolling  the  puddled  balls,  is  of  very 
inferior  quality.  Its  tenacity  is  so  low  that  it  is  quite  unfit 
for  axles  and  portions  of  machinery  which  have  to  resist  any 
strain,  and  it  could  not  be  drawn  into  wire.  Some  speci 
mens  of  puddled  bar  have  a  tensile  strength  as  low  as  9  tons 
per  square  inch,  whilst  the  best  varieties  of  bar  iron  have  a 
strength  of  upwards  of  25  tons.  The  fracture  of  such  bar 
exhibits  a  coarse  crystalline  structure,  which  is  generally 
found  to  indicate  inferior  tenacity.  The  hardness  of  puddled 


64        Metals :  their  Properties  and  Treatment. 

bars,  however,  is  greater  than  that  of  the  superior  varieties  of 
bar  iron,  and  this  quality  recommends  it  for  such  applica 
tions  as  the  construction  of  railway  lines  where  high  tenacity 
is  not  of  so  great  importance.  In  order  to  obtain  a  bar  iron 
of  better  quality,  the  puddled  bars  are  cut  up,  while  hot,  by 
large  shears,  into  lengths  of  a  foot  or  more,  according  to  the 
length  of  the  bar  required,  and  are  submitted  to  the  process 
of  fagotting  or  piling.  This  consists  in  placing  four  of  the 
lengths  upon  each  other,  so  as  to  form  a  pile  ;  this  is  placed 
in  a  re-heating  or  mill-furnace,  raised  to  a  welding  heat,  and 
passed  between  rollers  which  convert  the  four  bars  into  a 
single  bar,  to  be  drawn  out,  as  before,  to  the  required  dimen 
sions.  The  merchant  bar  thus  obtained  may  be  still  further 
improved  in  quality  by  a  repetition  of  the  process  of  rolling, 
which  is  generally  executed  upon  the  bars  doubled  upon 
themselves,  producing  the  toughest  description  of  wrought 
iron,  known  as  best  bar  or  wire  iron.  Such  iron  may  be 
bent  double,  in  a  cold  state,  or  a  bar  of  it  may  be  tied  into 
a  knot  when  cold  without  exhibiting  a  crack.  In  piling  iron 
for  boiler  plates,  cannon,  &c.,  the  bars  are  sometimes  placed 
crosswise  over  each  other  in  the  pile,  so  that  the  fibres  of 
one  layer  may  be  at  right  angles  with  the  fibres  of  the  next 
layer. 

The  Mill-furnace  or  Reheating-furnace  (Fig.  16)  employed 
for  raising  the  bars  to  a  welding  heat,  is  a  reverberatory 
furnace  so  constructed  that  as  little  air  as  possible  shall 
reach  the  hearth  without  having  previously  been  deprived  of 
oxygen  by  passing  through  the  fuel,  for  otherwise  a  large 
proportion  of  the  iron  would  be  wasted  in  the  form  of  oxide. 
The  furnace  has  only  one  opening  to  the  hearth,  through 
which  the  piles  of  iron  to  be  fagotted  are  introduced  ;  this 
opening  is  situated  immediately  under  the  chimney,  so  that 
when  the  door  is  opened  in  order  to  introduce  the  iron,  the 
air  which  is  drawn  through  it  passes  up  the  chimney  instead 
of  sweeping  over  the  hearth  of  the  furnace. 

Experiments  upon  a  particular  sample  of  puddled  bars, 


Improvement  of  Iron  by  Piling.  $$ 

having  a  tensile  strength  of  19^  tons  per  square  inch,  showed 
that  its  strength  increased  progressively  during  five  pro 
cesses  of  fagotting,  till  it  eventually  reached  27*.  tons,  when 
a  repetition  of  the  process  was  found  to  weaken  it  again, 
until,  after  the  eleventh  fagotting,  it  was  found  to  have 
returned  to  its  original  strength  of  19^  tons. 

The  coal  consumed  in  producing  one  ton  of  merchant  bar 


the  chfmney  *'*  Cntenng  by  ^  Chai"ging  d°°r  paSSCS  into 

iron  from  the  ore,  amounts  in  all  to  about  five  tons,  and 
every  reheating  for  the  process  of  piling  involves  the  con 
sumption  of  a  quantity  of  coal  equal  to  about  half  the 
weight  of  the  iron. 

The  great  improvement  in  the  strength  of  malleable 
iron  by  the  processes  of  fagotting  and  rolling  has  been 
more  satisfactorily  established  by  experience  than  explained 


66         Metals ;  their  Properties  and  Treatment. 

by  theory.  One  obvious  effect  of  the  violent  compres 
sion  between  the  rollers  is  the  squeezing  out  of  slag,  which 
is  liable  to  become  entangled  in  the  iron  during  the  ham 
mering  and  rolling  of  the  balls  taken  from  the  puddling- 
furnace.  The  occurrence  of  small  masses  of  slag  in  malle 
able  iron  is  not  an  uncommon  cause  of  weakness,  each 
particle  of  slag  giving  rise  to  a  flaw  in  the  metal.  In  the 
process  of  reheating  the  bars  this  slag  is  melted,  and  may 
then  be  squeezed  out  by  the  action  of  the  rollers. 

A  marked  diminution  in  the  proportions  of  carbon  and 
silicon  present  in  the  iron  is  also  effected  during  the  process, 
as  shown  by  the  following  results  of  chemical  analysis  : — 

In  100  parts  Carbon  Silicon 

Puddled  Bar      .         .         .     0-296  0-120 

Best  Bar    .         .         .         .     o-iii  0-088 

This  may  be  explained  by  the  action  of  the  oxide  of  iron 
formed  upon  the  surface  of  the  bar  during  exposure  to  air  at 
a  welding  heat  (see  p.  49). 

The  rolling  of  several  bars  into  a  single  bar  would  render 
the  structure  of  the  metal  uniform,  so  that  the  bar  would  be 
equally  strong  throughout. 

During  the  operations  of  fagotting  and  rolling,  the  iron 
acquires  a  remarkable  fibrous  structure,  so  that  if  a  bar  of 
the  best  iron  be  notched  with  a  chisel,  and  broken  across  by 
a  steady  pressure,  the  fracture  will  present  a  stringy  appear 
ance,  resembling  that  of  a  green  stick ;  whilst  a  puddled  bar 
thus  treated  would  exhibit  a  crystalline  shining  fracture,  not 
unlike  that  of  cast  iron.  That  this  nerve  or  reed,  as  the 
fibrous  structure  is  sometimes  called,  should  materially  in 
crease  the  resistance  of  a  bar  to  any  transverse  strain,  can 
readily  be  believed,  for  such  a  bar  resembles  a  bundle  of 
wires  firmly  bound  together,  whilst  a  crystalline  bar  must  be 
regarded  as  composed  of  a  number  of  particles  of  iron  stuck 
together  in  a  confused  manner.  But  with  our  present  im 
perfect  acquaintance  with  the  mutual  relations  and  move 
ments  of  the  individual  particles  composing  a  solid  mass,  it 


Fibrous  and  Crystalline  Iron. 


is  not  easy  to  give  a  satisfactory  explanation  of  the  produc 
tion  of  the  fibrous  structure  by  rolling  the  softened  bars  in 
the  direction  of  their  length.  Much  less  can  we  explain  the 
circumstance,  which  appears  to  have  been  satisfactorily 
established,  that  this  fibrous  structure  is  liable  to  re-con 
version  into  the  crystalline  structure  if  the  iron  be  subjected 
to  a  long  succes 
sion  of  powerful 
vibrations. 

The  deteriora 
tion  in  the  strength 
of  bar  iron  by  often - 
repeated  forging 
under  the  hammer, 
is  commonly  ex 
plained  as  resulting 
from  this  change  in 
structure;  and  axles, 
girders,  &c.,  origin 
ally  made  of  fibrous 
iron,  are  said  to 
have  snapped  unex 
pectedly,  exhibiting 
a  crystalline  struc 
ture.  Hence,  in 
cases  where  the 
iron  is  to  be  ex- 
Posed  to  much  vi- 
bration,  a  fine 
grained  wrought-iron  richer  in  carbon  is  preferred  to  a 
fibrous  iron. 

In  drawing  any  inference  as  to  the  quality  of  wrought  iron 
from  the  character  of  its  fracture,  it  is  most  important  that 
the  mode  of  breaking  it  should  be  taken  into  account,  for  it  is 
found  that  a  bar  or  plate  which  exhibits  a  fine  fibrous  struc 
ture  when  broken  by  bending,  appears  crystalline  when 

F  2 


FIG.  18. — Structure  of 
inferior  Bar  Iron. 


68         Metals  :  their  Properties  and  Treatment. 


suddenly  snapped,  or  when  broken  by  a  blow  from  a  shot; 
and  it  is  probable  that  a  want  of  attention  to  this  has  given 
rise  to  many  of  the  contradictory  statements  with  respect  to 
alterations  in  the  structure  of  wrought  iron  under  various 
conditions. 

Some  of  the  recent  experiments  upon  this  subject  lead  to 
the  conclusion  that  the  fibrous  fracture  of  the  best  descrip 
tions  of  bar  iron  is  due  to  their  ductility,  which  causes  them 
to  draw  out  before  breaking,  whereas  an  inferior  bar  snaps 
without  drawing  out,  the  suddenness  of  the  fracture  prevent 
ing  the  appearance  of  fibre. 

When  a  bar  of  the  best  iron  is  soaked  for  a  few  days  in 


FIG.  19. — Structure  of  Puddled  Bar 


very  weak  muriatic  or  nitric  acid,  its  fibrous  structure  is 
rendered  manifest,  and  it  presents  the  appearance  of  a  bundle 
of  fine  straight  fibres  laid  regularly  side  by  side  (Fig.  17).  In 
an  inferior  bar  (Fig.  18)  the  fibres  are  coarser  and  not  so 
regularly  arranged;  whilst  in  a  puddled  bar  (Fig.  19)  there 
is  little  or  no  regularity  of  structure  disclosed.* 

*  The  circumstance  that  the  fibre  resists  the  action  of  the  acid  longer 
than  the  metal  lying  between  the  fibres,  would  lead  a  chemist  to  suspect 
that  the  fibres  consist  of  crystallised,  and  the  interstitial  portion  of 
amorphous  (or  colloid}  iron.  It  is  a  common  observation  in  the 
laboratory  that  when  one  portion  only  of  a  mass  is  crystallised,  it  is 
much  less  readily  melted  or  dissolved  than  the  portion  which  is  not  in 
that  condition.  It  is  also  frequently  seen  that  the  uncrystallised  portion 
of  such  a  mass  is  converted  into  a  mass  of  crystals,  in  course  of  time,  or 
if  briskly  shaken  or  stirred.  How  far  'is  the  alleged  change  in  the 
structure  of  bar  iron  from  fibrous  to  crystalline  really  caused  by  the  crystal- 


Cold-short  and  Red-short  Iron.  69 

Bar  iron  which  cracks  when  doubled  or  tied  in  a  cold  state 
is  said  to  be  cold-short;  and  this  defect  is  very  frequently 
due  to  the  presence  of  phosphorus  in  the  metal.  Bar  iron 
commonly  contains  about  one-thousandth  of  its  weight  of 
phosphorus,  without  injury  to  its  strength,  and,  it  is  said,  with 
an  improvement  in  its  capacity  for  welding ;  but  when  the 
proportion  of  phosphorus  amounts  to  one  part  in  two  hun 
dred  of  iron,  its  effect  in  diminishing  the  tenacity  of  the 
iron  becomes  perceptible ;  and  when  it  reaches  one  and  a 
half  in  two  hundred,  it  renders  the  iron  decidedly  cold-short. 

The  cold-short  iron  loses  its  brittleness  at  a  high  tempera 
ture,  so  that  it  may  be  forged  with  great  readiness. 

The  fracture  of  iron  containing  so  large  an  amount  of 
phosphorus  is  commonly  found  to  present  a  coarsely  crystal 
line  structure. 

Silicon  is  said  to  injure  the  tenacity  of  bar  iron,  whether 
hot  or  cold,  in  a  higher  degree  than  phosphorus;  and  arsenic, 
which  is  occasionally  present,  renders  the  iron  cold-short 
and  hinders  welding. 

When  the  iron  cracks  while  being  worked  under  the 
hammer  at  a  welding  heat,  it  is  termed  hot-short  or  red-short, 
and  this  quality  is  often  exhibited  by  iron  which  is  sufficiently 
pure  to  be  very  tough  when  cold.  The  presence  of  sulphur 
has  a  decided  effect  in  causing  red-shortness,  even  if  there 
be  only  four  parts  in  ten  thousand  parts  of  iron ;  and  it  is 
alleged,  with  much  probability,  that  enough  sulphur  for  this 
purpose  is  sometimes  imparted  to  the  iron  by  the  products 
of  combustion  of  the  coal  in  the  reheating  furnace. 

There  appears  to  be  little  knowledge  of  a  thoroughly 
satisfactory  character  with  respect  to  the  effect  of  different 
proportions  of  foreign  matter  upon  the  quality  of  malleable 
iron,  for  the  exact  analysis  of  this  material  is  tedious  and 
difficult,  and  those  who  are  competent  to  execute  it  in  a 

lisation  of  the  colloid  portion  of  the  metal,  which  would  have  the  effect 
of  rendering  it  less  plastic  or  ductile,  and  more  liable  to  snap,  a  mode  of 
fracture  which  would  prevent  the  fibrous  structure  from  becoming 
visible  ? 


7O         Metals :  their  Properties  and  Treatment. 

trustworthy  manner  have  rarely  the  opportunity  of  becoming 
practically  acquainted  with  the  behaviour  of  the  metal  in  the 
workshop  and  the  forge. 

STEEL. 

The  difference  between  steel  and  wrought  iron  (or  soft 
iron,  as  it  is  sometimes  called)  is  chiefly  seen  in  their 
behaviour  when  raised  to  a  high  temperature  and  suddenly 
cooled  by  being  plunged  into  water;  when  wrought  iron 
undergoes  little  if  any  change ;  while  steel  is  rendered  almost 
as  hard  as  diamond,  and  so  brittle  that  it  snaps  off  if  an 
attempt  be  made  to  bend  it.  If  this  very  hard  brittle  steel 
be  again  heated  to  a  temperature  far  short  of  redness,  and 
cooled,  it  becomes  much  softer  than  before  and  extremely 
elastic,  so  that  when  forcibly  bent  it  springs  back  into  its 
former  position,  whereas  wrought  iron  would  retain  a  per 
manent  bend.  It  will  be  remembered  that  cast  iron  is  also 
greatly  hardened  by  being  suddenly  cooled,  but  it  cannot  be 
rendered  elastic  like  steel. 

The  property  of  being  hardened  by  chilling  is  dependent 
upon  the  presence  of  carbon  in  the  metal,  for  chemically 
pure  iron  does  not  exhibit  it,  though  all  specimens  of  com 
mercial  wrought  iron  are  slightly  hardened  when  so  treated, 
because  they  contain  a  small  proportion  of  carbon.  It  is, 
therefore,  difficult  to  define  the  exact  limit  beyond  which 
wrought  iron  passes  into  steel.  Bar  iron,  containing  as 
much  as  two  parts  of  carbon  in  a  thousand  of  metal,  would 
be  so  decidedly  hardened  by  chilling  as  to  be  termed  a 
steely  iron,  and  a  slight  increase  in  the  quantity  would  pro 
duce  a  mild  steel,  such  as  the  homogeneous  metal  of  which 
cannon  and  armour-plates  are  forged.  A  proportion  of 
carbon,  amounting  to  three  parts  in  the  thousand,  is  contained 
in  the  Bessemer  steel  rails,  and  in  the  steel  of  which  spades 
and  hammers  are  commonly  made.  Twice  this  proportion 
of  carbon,  or  six  parts  in  a  thousand,  is  contained  in  steel 
ramrods;  and  the  steel  employed  for  tools  commonly  con- 


Effects  of  the  presence  of  Carbon  on  Bar-iron.     71 

tains  ten  or  twelve  parts  of  carbon  in  a  thousand.  When 
the  carbon  amounts  to  fourteen  parts  in  a  thousand,  the 
steel  becomes  more  fusible  and  resembles  white  cast  iron. 

Bar  iron,  which  contains  only  a  minute  proportion  of 
carbon,  has  a  tensile  strength  of  about  57,500  Ibs.  (nearly 
26  tons)  per  square  inch*;  but  when  the  proportion  of 
carbon  amounts  to  three  or  five  parts  in  a  thousand,  its 
tensile  strength  is  increased  to  90,000  or  100,000  Ibs.  (40  tons 
or  45  tons)  per  square  inch,  while  it  is  still  soft  enough  to  be 
easily  punched  and  flanged.  Such  a  metal  is  well  suited 
for  boiler-plates  and  similar  purposes. 

For  armour-plates  designed  to  protect  ships,  by  offering 
resistance  to  blows  from  shot  at  high  velocities,  it  appears 
to  be  desirable  that  the  proportion  of  carbon  should  not 
exceed  two  parts  in  a  thousand,  for,  although  an  increased 
proportion  of  this  element  is  attended  with  increased  re 
sistance  to  tension  (or  to  a  force  tending  to  pull  the  particles 
of  the  metal  asunder),  as  well  as  to  penetration  by  dead 
pressure,  it  renders  an  armour-plate  more  liable  to  fracture 
under  the  sudden  and  powerful  blow  of  a  shot. 

In  addition  to  hardness  and  increased  tensile  strength, 
the  presence  of  carbon  confers  another  valuable  property 
upon  the  iron,  namely,  the  capability  of  retaining  magnetism. 
When  a  bar  of  soft  iron  is  placed  in  contact  with  a  magnet, 
or  in  the  axis  of  a  coil  of  wire  through  which  a  galvanic 
current  is  transmitted,  the  iron  bar  acquires  all  the  properties 
of  a  magnet,  becoming  capable  of  attracting  iron  filings, 
and,  if  freely  suspended,  of  pointing,  like  a  compass  needle, 
north  and  south.  It  loses  these  magnetic  properties  as  soon 
as  the  permanent  magnet  is  removed,  or  the  galvanic  cur 
rent  is  discontinued  in  the  surrounding  wire.  A  bar  of 
steel,  however,  would  retain  its  magnetic  properties.  Just 
as  all  specimens  of  commercial  bar  iron  are  slightly  hardened 
by  chilling,  in  consequence  of  their  containing  a  minute 

*  The  Board  of  Trade  gives  5  tons  per  square  inch  as  the  working 
strain  to  which  it  is  safe  to  expose  bar  iron  in  actual  practice. 


72         Metals :  their  Properties  and  Treatment. 

quantity  of  carbon,  so  they  are  all  slightly  retentive  of  mag 
netism  in  proportion  to  the  quantity  of  carbon  present.  In 
the  manufacture  of  electro -magnetic  instruments  of  various 
kinds,  the  action  of  which  depends  upon  the  sudden  loss  of 
magnetic  power  by  a  bar  of  iron  when  the  galvanic  current 
is  interrupted,  it  becomes  of  great  importance  to  select  the 
softest  commercial  iron,  so  that  it  may  lose  its  magnetic 
power  as  quickly  as  possible.  On  the  other  hand,  the  hardest 
steel  is  selected  for  the  production  of  permanent  magnets, 
and  it  has  been  noticed  that  the  addition  of  the  metal 


FIG.  20. — Cementation  Furnace  for  converting  Bar  Iron  into  Steel. 

tungsten  to  steel  increases  its  power  of  retaining  magnetism. 

Steel  rings  when  struck,  much  more  than  iron,  and  this 
property  is  relied  upon  by  the  steel-maker  as  one  of  the  tests 
of  its  quality. 

Conversion  of  Bar  Iron  into  Steel  by  Cementation. — 
The  process  of  cementation  by  which  until  lately  nearly 
all  English  steel  was  produced,  consists  in  heating  bar  iron 
in  contact  with  charcoal,  in  a  closed  chest,  until  it  has 
acquired  a  proper  proportion  of  carbon. 

The  cementation  furnace  (Fig.  20)  is  dome-shaped,  like 
the  furnace  of  a  glass-house,  and  is  enclosed  in  a  conical 


Production  of  Steel  by  Cementation.  73 

jacket  of  brick-work  which  serves  to  carry  off  the  smoke 
from  the  flues.  The  hearth  of  the  furnace  is  divided  into 
two  parts  by  the  grate  G,  traversing  the  whole  length  (13  or 
14  feet)  of  the  furnace,  in  which  a  coal  fire  is  maintained, 
the  flame  of  which  is  made  to  circulate  above,  below,  and 
around  the  fire-clay  chests  or  pots,  or  troughs  c  placed  one 
on  each  side  of  the  grate,  before  escaping  through  the  flues 
in  the  wall  H  and  through  the  opening  M.  These  troughs 
are  10  or  12  feet  long,  and  about  3  feet  in  depth  and  width, 
so  that  each  will  contain  seven  or  eight  tons  of  bar  iron, 
together  with  the  charcoal  necessary  for  its  conversion  into 
steel.  A  small  opening  is  left  at  about  the  middle  of  one 
end  of  each  chest,  through  which  the  end  of  one  of  the  bars 
undergoing  cementation  is  allowed  to  project;  this  proof-bar 
is  withdrawn  from  time  to  time,  through  a  small  door  in  the 
wall  of  the  furnace,  for  the  purpose  of  watching  the  progress 
of  the  cementation.  There  is  also  a  small  door  in  the  wall 
of  the  furnace,  a  little  above  the  top  of  each  trough,  through 
which  the  bars  of  iron  may  be  introduced  and  withdrawn,  a 
larger  door  being  made  in  the  middle  of  the  wall  to  allow 
the  passage  of  the  workmen. 

The  nature  of  the  cement  or  carbonaceous  material  em 
ployed  varies  in  different  works,  but  the  bulk  of  it  nearly 
always  consists  of  ground  charcoal  from  hard  wood,  with 
which  there  are  sometimes  mixed  a  little  common  salt  and 
some  ashes  of  the  charcoal.  The  salt  and  the  alkaline 
matters  contained  in  the  ashes  are  believed  by  some  persons 
to  have  a  beneficial  effect  in  converting  into  a  glass  the 
silica  which  is  contained  in  the  charcoal,  and  thus  preventing 
it  from  imparting  silicon  to  the  steel.  The  bars  of  iron 
should  be  of  the  purest  description  if  the  best  steel  is  to  be 
produced.  They  are  about  three  inches  broad,  and  one- 
third  of  an  inch  thick. 

In  order  to  fill  the  troughs,  the  workman  stands  upon  an 
iron  platform  between  the  two,  and  sifts  the  cement  powder 
into  them,  so  as  to  form  a  layer  of  about  half  an  inch  in  depth, 


74        Metals :  their  Properties  and  Treatment. 

upon  which  the  bars  are  arranged,  standing  upon  their  edges, 
at  about  an  inch  apart.  More  cement  powder  is  now  sifted 
over  these,  so  as  to  fill  up  the  intervals  between  them,  and 
to  cover  them  entirely  to  the  depth  of  about  an  inch.  Upon 
this  a  second  layer  of  bars  is  placed,  then  more  of  the 
charcoal  powder,  and  so  on  until  the  trough  is  filled  to  within 
a  few  inches ;  it  is  then  covered  in  with  four  or  five  inches 
of  fire-clay  or  some  similar  material,  well  rammed  down,  and 
the  fire  is  gradually  applied  during  the  first  two  or  three 
days,  to  avoid  the  risk  of  splitting  the  troughs.  A  tempera 
ture  high  enough  to  melt  copper  (estimated  at  about  2,000° 
of  Fahrenheit's  scale)  is  required  to  enable  the  bar  iron  to 
acquire  a  proper  proportion  of  carbon,  and  the  troughs  are 
maintained  at  this  temperature  for  a  period  proportionate  to 
the  hardness  which  the  steel  is  required  to  possess ;  four  days 
being  sufficient  for  producing  the  steel  of  which  saws  and 
springs  are  made,  while  six  or  eight  days  are  required  for 
shear  steel,  and  ten  days  or  more  are  required  for  the  very 
hard  steel  of  which  cold  chisels  are  made.  The  fire  is  then 
gradually  let  down,  to  avoid  sudden  change  of  temperature, 
so  that  some  days  elapse  before  the  troughs  are  cool  enough 
to  be  opened.  About  three  weeks  are  commonly  occupied 
in  the  conversion  of  the  bar  iron  into  steel — one  to  get  up 
the  heat,  one  to  keep  it  at  the  required  degree,  and  one  to 
cool  it  down ;  so  that  only  about  sixteen  cementations  can 
be  executed  in  a  year  by  a  single  furnace. 

The  bars  are  found  to  have  upon  their  surface  bubbles  or 
blisters  of  considerable  size,  whence  they  are  called  blister  steel. 
On  breaking  the  bars,  the  fracture  exhibits  a  silvery  lustre 
and  a  well-marked  crystalline  structure.  The  proportion  of 
carbon  which  has  entered  into  combination  with  the  iron 
depends  upon  the*  duration  of  the  cementing  process,  but  it 
rarely  exceeds  fourteen  parts  in  a  thousand  parts  of  the  metal. 

The  chemical  changes  which  are  involved  in  the  process 
of  cementation  are  not  yet  thoroughly  understood.  The 
passage  of  the  infusible  solid  carbon  into  the  interior  of  the 


Theory  of  the  Cementation  Process.  75 

solid  iron  bar  obviously  requires  explanation.  It  might  be 
imagined  that  the  external  particles  of  iron  which  are  in 
contact  with  the  charcoal,  becoming  surcharged  with  carbon, 
impart  a  portion  of  that  element  to  the  next  layer,  and  so 
on,  until  the  particles  in  the  very  centre  of  the  bar  had 
acquired  a  proper  share  of  carbon ;  but  such  an  explanation 
would  require  that  the  outside  of  the  bar,  at  the  close  of  the 
process,  should  be  very  much  richer  in  carbon  than  the 
inside,  and  we  have  no  evidence  that  this  is  the  case. 

The  following  explanation  appears  more  probable.  The 
small  quantity  of  oxygen  contained  in  the  air  remaining  in 
the  trough,  and  present  in  the  pores  of  the  charcoal,  enters 
into  combination  with  the  carbon  to  form  carbonic  oxide 
gas;  this  gas,  in  contact  with  iron  at  a  high  temperature, 
gives  up  one-half  of  its  carbon  to  the  metal,  and  becomes 
converted  into  carbonic  acid  gas ;  but  this  carbonic  acid,  in 
contact  with  the  strongly-heated  carbon,  is  reconverted  into 
carbonic  oxide,  which  again  transfers  one-half  of  its  carbon 
to  the  metal,  these  changes  recurring  many  times  in  the 
same  order  until  the  whole  of  the  iron  is  converted  into 
steel.  The  observations  of  chemists  during  the  last  few 
years  have  shown  that  red-hot  iron  allows  the  passage  of  gas 
through  its  substance,  and  that  this  metal  has  the  power  of 
absorbing  a  considerable  quantity  of  carbonic  oxide,  which 
renders  it  easy  to  account  for  the  transference  of  carbon 
from  the  charcoal  into  the  interior  of  the  bar. 

Other  gases  containing  carbon  are  capable  of  imparting 
that  element  to  iron ;  thus,  if  coal  gas,  which  contains  carbon 
in  combination  with  hydrogen,  be  passed  for  an  hour  through 
an  iron  tube  containing  some  soft  iron  wires  heated  to 
bright  redness,  the  wires  will  absorb  carbon  from  the  gas 
and  become  converted  into  steel. 

The  blisters,  which  are  distributed  sparsely  and  irregularly 
over  the  surface  of  the  bars,  are  commonly  believed  to  be 
due  to  the  action  of  particles  of  oxide  of  iron,  or  of  slag, 
accidentally  occurring  in  the  iron  bars,  upon  the  carbon 


76         Metals:  their  Properties  and  Treatment. 

combined  with  the  iron,  giving  rise  to  carbonic-oxide  gas, 
which  escapes  as  a  bubble  through  the  softened  iron. 

As  might  be  anticipated,  the  blistered  steel,  in  its  present 
condition,  is  only  fitted  for  very  rough  articles,  such  as 
shovels ;  its  largely  crystalline  structure  renders  it  deficient 
in  tenacity,  and  the  bars  are  further  weakened  by  their  want 
of  uniformity  and  by  the  presence  of  the  blisters. 

Conversion  of  Blistered  Steel  into  Tilted  or  Shear  Steel. — 
The  quality  of  the  blister  steel  is  improved  by  a  process 
similar  in  principle  to  the  fagotting  of  bar  iron.  Five  bars 
of  blister  steel  are  bound  together  into  a  bundle,  being 
secured  by  a  stout  steel  wire ;  four  of  the  bars  are  about  18 
inches  long,  and  the  fifth  is  twice  that  length,  so  that  it  pro 
jects  beyond  the  others  and  forms  a  handle.  This  bundle 
is  raised  to  a  welding  heat  in  a  forge,  sprinkled  with  sand  to 
combine  with  the  oxide  of  iron  and  form  a  fusible  slag 
(see  p.  49),  and  placed  under  the  tilt-hammer ;  this  hammer 
weighs  about  two  hundredweight,  and  it  is  so  suspended  that 
it  may  be  raised  by  cams  projecting  from  the  circumference 
of  a  wheel,  the  revolutions  of  which  bring  them  down  in 
succession  upon  the  tail  of  the  hammer,  the  head  falling  again 
upon  the  anvil  as  soon  as  the  cam  has  passed.  A  few  blows 
from  this  hammer  soon  weld  the  bars  together,  when  the 
binding  ring  is  knocked  off,  the  bundle  again  heated  in  the 
forge,  and  hammered  or  tilted  throughout  its  whole  length, 
and  on  all  sides,  until  it  is  reduced  to  a  rectangular  bar  of 
the  right  dimensions.  In  order  to  avoid  the  necessity  for 
reheating  the  bar  during  the  process,  the  tilting  must  be 
effected  with  great  celerity,  and  the  hammer  is  made  to 
deliver  300  or  400  blows  per  minute,  the  number  being,  of 
course,  regulated  by  the  rate  at  which  the  cam-wheel  revolves. 
The  workman  being  seated  upon  a  swinging  bench  which 
brings  him  upon  a  level  with  the  anvil,  is  enabled  to  move 
to  and  fro  with  little  effort,  and  to  bring  every  part  of  the 
elongated  bar  under  the  strokes  of  the  hammer.  The 
fracture  of  a  bar  of  shear  steel  shows  it  to  possess  a  much 


Cast  Steel. 


77 


FIG.  21. 


more  compact  structure  than  the  blister  steel,  and  its  tena 
city  and  ductility  have  been  much  improved  by  the  tilting. 
It  is  probable  also  that,  as  in  forging  bar  iron, 
the  proportion  of  carbon  has  undergone  a  slight 
diminution,  the  steel  being  found  to  become 
softer  after  repeated  tilting.  If  double  shear 
steel  be  required,  the  tilted  bar  is  broken  and 
the  two  pieces  welded  into  a  single  bar. 

Shear  steel  derives  its  name  from  its  use  in 
making  certain  large  shears,  and  it  is  commonly 
employed  for  tools  which  are  to  possess  con 
siderable  toughness,  without  being  extremely 
hard,  such  as  scythes,  plane-irons,  and  large  knives ;  but  its 
deficient  hardness  prevents  it  from  taking  a  very  high  polish 
or  a  very  keen  edge,  so  that  it  will  not  serve  for  the  finer 
kinds  of  cutlery. 
The  best  variety  of 
steel  used  for  these 
is  made  by  melting 
the  blister  steel  and 
casting  it  into  ingots. 

Conversion  of  JB lis 
ter  Steel  into  Cast 
Steel.  —  The  blister 
steel  is  broken  up 
into  pieces  of  a 
convenient  size  for 
packing  close  to 
gether,  and  about 
30  Ibs.  of  it  are  in 
troduced  into  a  tall 
narrow  crucible  (Fig.  FIG  22_Furnace  d  Pot  for  meltmg  bteel. 

2l)     about    tWO     feet  ^,Grate.     c,  Crucible.    6,  Cover  of  Furnace. 

.  .  %'  ,  ,.     ,.  a,  Chimney. 

high,  made   of  fire 
clay  mixed  with  black-lead,   and  provided  with  a  closely- 
fitting    cover.      Some    steel-makers    add    a    little    bottle- 


78         Metals :  their  Properties  and  Treatment. 

glass  to  fuse  over  the  surface  and  prevent  oxidation  of  the 
steel. 

The  crucibles  are  placed  in  a  small  furnace  (Fig.  22) 
holding  six,  twelve,  or  more,  about  one  foot  wide  and  two  feet 
deep,  the  opening  of  which  is  usually  on  a  level  with  the 
floor,  to  facilitate  the  lifting  of  the  crucibles.  Several  of 
these  furnaces  are  connected  by  flues  with  the  high  chimney 
of  the  works,  so  that  a  powerful  draught  may  be  produced. 
Hard  coke  broken  into  small  pieces  is  employed  to  raise  the 
crucible  to  a  bright  red  heat;  the  steel  is  then  introduced, 
the  crucible  covered,  and  the  furnace  filled  up  with  coke; 
when  the  steel  is  melted,  the  crucible  is  lifted  out  with  a 
pair  of  tongs,  and  its  contents  pou-red  into  a  rectangular  or 
octagonal  mould  of  cast  iron  which  has  been  previously 
heated  and  is  placed  vertically  for  the  steel  to  be  poured  in. 
The  mould  is  made  in  two  halves,  closely  fitting  together, 
so  that  it  may  be  opened  for  the  removal  of  the  bar  of  cast 
steel,  and  is  coated  inside  with  coal-tar  soot.  The  quality 
of  the  cast  steel  produced  is  in  some  measure  dependent 
upon  the  temperature  at  which  it  is  poured,  so  that  an 
experienced  workman  is  employed  for  the  purpose. 

For  the  production  of  large  castings  of  steel  in  this  way, 
the  requisite  number  of  crucibles  must  be  emptied  into  the 
mould  as  nearly  as  possible  at  the  same  time.  At  the  factory 
of  Krupp  at  Essen,  near  Cologne,  a  casting  of  16  tons  may 
be  produced  in  this  way,  400  men  being  well  drilled  to  co 
operate  in  emptying  1,200  crucibles,  so  that  the  melted  steel 
may  flow  in  an  uninterrupted  stream  along  the  gutters  leading 
to  the  mould.  Great  alterations  and  improvements  in  the 
manufacture  of  cast  steel  will  probably  result  from  the  intro 
duction  of  the  regenerative  gas-furnace  of  Siemens,  in  which 
steel  may  be  easily  melted  in  large  quantities. 

Cast  steel  is  much  more  uniform  in  structure  than  tilted 
steel,  and  has  a  very  compact  granular  texture,  without  lustre, 
indicating  high  tenacity,  as  may  be  seen  on  inspecting  its 
fracture  ;  though  here,  as  in  the  case  of  bar  iron  (p.  67),  it 


Heath's  Process.  79 

must  be  borne  in  mind,  that  when  fracture  takes  place  slowly, 
it  will  present  a  more  or  less  distinctly  fibrous  appearance; 
the  granular  structure  becoming  evident  only  on  sudden 
fracture.  The  higher  the  quality  of  the  steel,  the  finer  is  the 
granular  structure  exhibited  by  sudden  breaking.  The  lower 
qualities  somewhat  resemble  bar  iron  in  fracture.  When 
produced  by  the  process  just  described,  cast  steel  has  the 
serious  defect  of  being  brittle  at  a  high  temperature,  so  that 
it  is  forged  with  difficulty,  and  does  not  admit  of  being 
welded.  But  a  method  of  correcting  this  was  patented  by 
Heath,  in  1839,  which  consists  simply  in  adding  to  the  cast 
steel,  in  the  melting-pot,  about  one-hundredth  of  its  weight  of 
carburet  of  manganese,  the  result  of  the  action  of  heat  upon 
a  mixture  of  black  oxide  of  manganese  (ore  of  manganese) 
and  charcoal,  or  some  other  substance  containing  carbon, 
such  as  coal  tar.  After  this  addition,  the  cast  steel  possesses 
much  more  tenacity  at  a  high  temperature,  and  can  be 
welded  either  to  itself  or  to  wrought  iron,  so  that  it  may  be 
employed  for  the  fabrication  of  many  implements  which 
were  formerly  obliged  to  be  made  of  shear  steel.  Thus,  the 
blades  of  table  knives  can  be  made  of  cast  steel  welded  on 
to  an  iron  tang,  as  that  part  of  the  knife  is  called  which  is 
fixed  into  the  handle. 

Another  important  consequence  of  the  introduction  of 
Heath's  process  has  been  a  reduction  of  about  one-third  in 
the  price  of  cast  steel,  by  enabling  it  to  be  produced  from  an 
inferior  quality  of  bar  iron,  instead  of  the  very  expensive 
descriptions  which  it  was  necessary  to  employ  previously  to 
this  discovery. 

The  mode  in  which  this  addition  of  manganese  acts  to 
produce  so  great  an  improvement  in  the  quality  of  the  cast 
steel  is  by  no  means  understood.  It  does  not  appear  to 
depend  upon  the  formation  of  an  alloy  of  manganese  with 
the  steel,  for  the  bulk  of  that  metal  is  found  in  the  slag 
from  the  melting-pots,  only  a  minute  proportion  entering 
into  the  composition  of  the  steel ;  but  that  even  this  small 


8o         Metals :  their  Properties  and  Treatment. 

quantity  affects  the  quality  of  the  metal,  appears  to  have 
been  proved  by  the  •  observation  that  the  manganiferous 
steel,  if  melted  a  second  time,  becomes  as  red-short  as  if  no 
manganese  had  been  added,  probably  because  the  small 
proportion  of  that  metal  is  removed  by  the  oxygen  of  the  air 
during  the  re-melting.  It  is  commonly  believed  that  man 
ganese  has  a  particular  tendency  to  encourage  the  removal 
of  sulphur,  phosphorus,  and  silicon  in  the  slag  both  from 
steel  and  iron,  though  its  precise  mode  of  action  has  not 
been  defined  (see  p.  61). 

For  the  manufacture  of  some  tools  requiring  rough  usage, 
such  as  the  chisels  of  planes,  it  is  customary  to  employ  a  bar 
of  iron  faced  with  steel,  the  cutting  edge  being,  of  course, 
made  upon  the  steel  side,  which  receives  great  support  from 
the  wrought  iron.  To  produce  such  a  compound  bar,  a  bar 
of  iron  is  polished  upon  that  surface  which  is  to  be  faced 
with  steel,  heated  to  redness,  sprinkled  with  borax  to  cleanse 
the  oxide  from  its  surface,  and  placed  in  the  ingot  mould 
destined  to  receive  the  cast  steel,  which  then  adheres  firmly 
to  the  polished  iron,  so  that  the  two  may  be  forged  together. 

Production  of  Bessemer  Steel. — It  has  been  already  stated 
that  Bessemer's  process  for  converting  cast  iron  into  mal 
leable  iron  depends  upon  the  removal  of  the  carbon  by 
forcing  air  through  the  liquid  metal,  and  that  if  this  process 
be  arrested  before  the  removal  of  the  carbon  is  completed, 
the  metal  will  have  the  composition  of  steel.  Another 
process  by  which  this  kind  of  steel  is  produced  consists  in 
depriving  the  cast  iron  of  nearly  the  whole  of  its  carbon,  so 
as  to  obtain  wrought  iron,  which  is  then  converted  into 
steel  by  adding  the  proper  proportion  of  carbon  in  the  form 
of  Spiegel-eisen. 

The  converter  (Fig.  23)  in  which  this  process  is  carried 
out  is  made  of  wrought  iron  boiler-plate,  and  lined  with  fire 
clay  or  other  refractory  material  to  protect  it  from  oxidation. 
It  is  sometimes  large  enough  to  contain  ten  tons  of  cast  iron 
for  a  charge,  and  is  suspended  on  trunnions  so  that  it  may 


Bessemer  s  Process. 


81 


be  easily  tilted  for  charging   and   discharging.     A  six-ton 
converter  is  1 1  feet  high  and  5^-  feet  in  its  widest  diameter. 
Through  the  bottom  of  this  vessel  there  are  several  openings 
to  admit  the  blast  of  air,  which  is  blown  in  at  a  pressure  of 
fifteen  or  twenty  pounds  upon  the  inch  through  35  holes,  from 
7  tuyeres  with  5  holes  each.     The  converter  having  been 
heated  by  burning  a  little  fuel  within  it,  is  charged  with  pig 
iron  which  has  been  previously 
melted  in  a  separate  furnace. 
a  pig  iron  containing  a  large 
proportion  of  graphite  and  a 
small   proportion    of  sulphur 
and  phosphorus  being  selected. 
The  air,  bubbling  through  the 
liquid  metal,  induces   an   in 
tense  combustion  of  the  iron, 
producing  a  large  quantity  of 
the  black  or  magnetic   oxide 
of  iron  which    is  carried   up 
by  the  force  of  the  blast  to 
gether  with   the    nitrogen   of 
the  air,   which   does   not   act 
upon  the  iron.     The  bubbles 
of  this   gas   being  forced   up 
through  the  melted  metal,  ef 
fectually  mix  the   unoxidised 
portion  with  the  melted  oxide, 
which  converts  the  carbon  of 
the  cast  iron  into  carbonic  oxide 
gas,  and  the  silicon  into  silicic  acid,  the  latter  combining  with 
some  oxide  of  iron  to  form  a  slag  which  appears  as  a  froth 
at  the  mouth  of  the  converter.     The  silicon  is  always  oxi 
dised  before  the  carbon,  and  during  the  first  ten  minutes  or 
so,  very  little  flame  appears  at  the  mouth  of  the  converter 
>mce,  in  this  process,  a  portion  of  the  iron  itself  is  the  fuel 
lergoing   combustion,    the  temperature   is   much  higher 


FIG.  23. — Bessemer's  Converting 
Vessel. 


82         Metals ;  their  Properties  and  Treatment. 

than  that  of  the  puddling  furnace,  in  which  coal  is  the  fuel, 
for  a  given  quantity  of  oxygen,  in  the  act  of  burning  iron, 
produces  above  one-third  more  heat  than  in  the  act  of  burn, 
ing  carbon.  The  temperature  produced  in  the  converter  is 
able  to  effect  the  complete  fusion  of  the  purified  iron,  which 
remains  liquid  throughout  the  operation  instead  of  sepa 
rating  in  a  pasty  form  as  in  the  process  of  puddling.  The 
manifestation  of  energy  during  the  conversion  is  very 
striking ;  the  roaring  of  the  blast  in  passing  through  the 
molten  iron,  the  long  flame  of  the  carbonic  oxide,  variegated 
by  the  combustion  of  small  quantities  of  metals,  the  bril 
liant  scintillations  from  the  iron,  and  the  white  hot  flakes 
of  slag  whirled  upward  by  the  blast  combine  to  produce  a 
volcanic  effect  which  is  not  easily  forgotten. 

The  operation  usually  lasts  for  only  twenty  minutes,  its 
termination  being  indicated  by  the  almost  total  disappear- 
ance  of  the  flame  of  carbonic  oxide,  but  a  far  more  exact 
method  of  ascertaining  when  the  requisite  amount  of  carbon 
has  been  removed,  consists  in  viewing  the  flame  through  an 
optical  instrument  known  as  the  spectroscope,  which  enables 
the  observer  to  detect  a  certain  line  in  the  spectrum  or  image 
of  the  flame,  the  disappearance  of  which  line  marks,  to 
within  a  few  seconds,  the  conclusion  of  the  process. 

If  Bessemer  iron  were  required,  the  contents  of  the  con 
verter  would  now  be  discharged  into  a  ladle  (Fig.  24)  and 
thence  into  moulds  having  the  form  of  the  required  bars,  but 
it  has  been  already  explained  that  the  necessity  for  employ 
ing  a  high-priced  pig  iron  prevents  the  economical  applica 
tion  of  this  otherwise  excellent  process  to  the  production  of 
malleable  iron  in  this  country. 

In  order  to  convert  the  decarbonised  metal  into  steel,  the 
requisite  proportion  of  carbon  is  added  in  the  form  of  Spicgcl- 
eisen  or  specular  iron  (which  must  not  be  confused  with  the 
specular  ore}.  This  may  be  defined  as  a  special  variety  of 
white  cast  iron  containing  a  large  quantity  of  carbon  in 
chemical  combination,  together  with  much  manganese.  It 


Bessemer1  s  Process. 


6  2 


84         Metals  :  their  Properties  and  Treatment. 

is  obtained  by  smelting,  in  a  blast-furnace  with  charcoal,  a 
spathic  iron  ore  containing  a  large  proportion  of  manganese. 
The  result  of  the  analysis  of  a  sample  of  this  material  is  here 
given. 

Spiegel-eisen. 

Iron  .  .  .  .  .  82-86 
Manganese  .  .  .  .1071 
Silicon  .....  I'OO 
Carbon  .....  4-32 


The  German  name  Spiegel-eisen  (mirror-iron)  alludes  to 
the  brilliant  silvery  lustre  of  the  metal,  the  fracture  of  which 
exhibits  a  foliated  crystalline  appearance  of  great  beauty. 
The  presence  of  manganese  is  probably  of  importance  with 
regard  to  the  use  of  Spiegel-eisen  as  an  ingredient  of  Besse 
mer  steel.  It  is  introduced  in  a  melted  state,  in  the  pro 
portion  of  about  i  part  to  30  parts  of  the  pig  iron  employed, 
into  the  converter,  which  is  tilted  into  a  horizontal  position 
to  receive  it,  the  blast  being  interrupted  during  the  addition, 
and  afterwards  turned  on  again,  for  a  few  seconds,  when  the 
converter  has  resumed  its  former  position,  in  order  to  diffuse 
the  Spiegel-eisen  through  the  liquid  iron,  after  which  the 
steel  is  transferred  to  the  moulds,  being  poured,  for  that 
purpose,  into  a  large  iron  ladle  lined  with  loam  (H,  Fig.  25) 
which  is  swung  under  the  converter  by  a  crane  (G),  and, 
after  receiving  the  metal,  is  swung  back  over  the  wrought 
iron  ingot  moulds  (K),  the  steel  being  run  out  by  raising  a 
fire-clay  plug  in  the  bottom  of  the  ladle. 

In  making  a  large  casting,  the  ingot  mould  employed  is  so 
massive  as  to  be  equal  in  weight  to  the  metal  required  to  be 
cast  in  it,  so  that  it  may  cool  the  ingot  quickly,  and  prevent 
the  formation  of  large  crystals  in  the  metal. 

Another  and  more  recent  form  of  converter  suggested  by 
Bessemer,  shown  in  Figs.  26,  27,  has  a  globular  form  and 
seven  feet  in  diameter,  the  air-blast  being  introduced  through 
a  single  tuyere  passed  through  the  top  of  the  converter,  and 


Bessemer 's  Process. 


86         Metals :  their  Properties  and  Treatment. 

made  of  circular  fire-bricks  (D,  Fig.  27)  strengthened  by  a 
stout  iron  rod  passing  down  the  centre,  and  terminating  in  a 
kind  of  rosette  with  numerous  apertures,  through  which  the 
air  is  projected  into  the  liquid  iron.  When  the  conversion 
is  finished,  the  tuyere  is  lifted  out  by  an  ingenious  hydraulic 
crane  (E),  and  the  converter  tipped  by  the  action  of  a 
hydraulic  ram,  in  order  to  discharge  its  contents  into  the 
casting-ladle.  It  is  said  that  two  such  converters  are  capable 


FIG.  26.— Bessemcr's  globular  Converting  Vessel. 

of  producing  200  tons  of  cast  steel  weekly,  which  would 
require,  by  the  old  process  of  melting  blistered  steel,  4,730 
crucibles,  and  760  melting  furnaces. 

In  order  to  secure  perfect  uniformity  in  the  composition 
and  therefore  in  the  quality  of  the  Bessemer  steel,  the  prac 
tice  has  been  introduced  of  actually  weighing  the  casting- 
ladle,  running  the  fused  malleable  iron  from  the  converter 
into  it,  and  then  weighing  it  a  second  time  to  ascertain  pre 
cisely  the  quantity  of  metal  introduced,  the  calculated  pro- 


Manufacture  of  Bessemer  Steel.  87 

portion  of  Spiegel-eisen  being  then  added  in  a  melted  state, 
and  mixed  with  the  iron  by  a  mechanical  agitator  made  of 
iron  coated  with  loam,  which  is  made  to  rotate  rapidly  in 
reverse  directions  for  three  or  four  minutes,  before  tipping 
the  steel  into  the  ingot-moulds.  To  obtain  a  sufficient 
quantity  of  Spiegel-eisen  of  uniform  composition,  the  melted 
metal  is  run  from  the  blast-furnace  on  to  a  revolving  table 
which  divides  it  into  drops  and  scatters  them  into  a  cistern 


27.— Section  of  Bessemer's  globular  Converting  Vessel.     A,  Th 

verier.     B,  Pulley  wheel  for  tipping  the  converter,  connected  by  a  wire 

rope  with  a  hydraulic  ram.  G,  Pipe  conveying  the  blast.     H,  Elbow- 
pipe  with  telescopic  joint. 

of  water,  so  that  they  become  converted  into  granules  like 
shot.  By  mixing  well  together,  say  500  tons  of  granulated 
Spiegel-eisen,  so  as  to  obtain  a  perfectly  uniform  mixture,  it 
is  ensured  that  each  charge  added  to  the  iron  in  the  con 
verter  will  contain  the  same  proportion  of  manganese,  silicon 
and  carbon.  The  granulated  metal  is  not  melted,  which 
would  cause  an  alteration  in  its  composition  by  the  oxidising 
action  of  the  air,  but  is  merely  heated  to  redness,  out  of 


88         Metals :  their  Properties  and  Treatment. 

contact  with  the  air,  in  a  kind  of  crucible,  whence  it  is 
allowed  to  drop,  through  a  pipe,  into  the  liquid  wrought  iron 
which  has  been  weighed  in  the  casting-ladle. 

The  extensive  manufacture  of  cast-steel  rails  by  the 
Bessemer  process  has  led  to  a  very  perfect  organisation  of 
the  works.  The  cast  iron  is  run  direct  from  the  blast-fur 
nace,  into  a  i2-ton  ladle  mounted  on  wheels,  and  taken  to 
the  converting-house,  where  there  are  six  vessels,  each  ca 
pable  of  converting  5  tons.  The  5  tons  of  steel  are  run 
from  the  casting-ladle  into  twenty  ingot  moulds,  so  that 
each  ingot  weighs  5  cwt  These  ingots,  when  removed 
from  the  mould,  are  reheated  in  a  reverberatory  furnace,  the 
hearth  of  which  is  fixed  on  a  spindle  by  which  it  is  made  to 
revolve  slowly  (once  in  two  minutes)  so  that  the  flame  of 
the  coal  fire  may  act  equally  upon  all  the  ingots  standing 
separately,  on  end,  and  bring  them  to  the  proper  tempera 
ture  for  the  rolling  mill.  The  railway  lines  of  cast  steel  are 
far  more  durable  than  those  laid  with  puddled  bars.  These 
old  wrought-iron  rails  are  capable  of  being  converted  into 
steel,  by  cutting  them  up,  heating  them  to  redness  with  a 
little  fuel,  in  the  converter  itself,  and  running  the  melted 
cast  iron  in  upon  them  ;  when  the  blast  is  turned  on  they 
soon  dissolve,  and  are  converted  into  steel  like  the  rest  of 
the  metal. 

100  tons  of  pig  iron,  treated  by  the  puddling  process, 
yield  75  tons  of  railway  bars,  whilst  85  tons  of  steel  bars 
are  obtained  by  Bessemer's  process.  The  very  large  steel 
ingots,  sometimes  8  feet  long  and  3  feet  square,  and  weigh 
ing  15  tons,  obtainable  by  this  process,  cannot  be  properly 
forced  under  the  steam-hammer,  so  that  a  most  ingenious 
combination  of  hammer  and  press  worked  by  hydraulic 
power  has  been  devised  for  the  purpose. 

Cast-steel  shot,  weighing  300  Ibs.  each,  are  made  by  cut 
ting  off  pieces  from  a  solid  cylinder  of  steel  softened  by  heat, 
moulding  them  by  pressure  between  curved  surfaces,  and 
rolling  them  between  two  iron  tables  with  corresponding 


Heatoris  Steel.  89 

grooves  of  hemispherical  section.  The  lower  table  is  forced 
with  immense  pressure  against  the  upper  one  by  the  hydrau 
lic  ram,  and  is  at  the  same  time  slowly  turned  on  its  axis. 
Three  balls  are.  made  at  once  in  little  more  than  as  many 
minutes. 

The  effect  of  hammering  or  rolling  in  augmenting  the 
tensile  strength  of  the  cast  steel  obtained  by  Bessemer's  pro 
cess  is  much  greater  than  in  the  case  of  malleable  iron  (See 
p.  65),  for  the  ingots  of  Bessemer  steel  which  gave  a  mean 
tensile  strength  of  27^  tons  per  square  inch,  had  it  increased 
to  68^  tons  by  hammering  or  rolling. 

It  is  alleged  by  those  who  are  well  acquainted  with  the 
art  of  steel-making,  that  the  presence  of  a  minute  proportion 
of  silicon  in  steel  is  essential  to  the  production  of  sound 
ingots,  for  that  when  this  element  is  entirely  absent,  the  steel 
disengages  gas  as  it  cools  in  the  mould,  and  boils  up  with 
great  violence,  an  effect  which  is  prevented  by  the  addition 
of  \  part  of  silicon  to  1,000  parts  of  steel.  The  silicon 
present  in  the  Spiegel-eisen  employed  in  Bessemer's  process 
is  therefore  regarded  as  of  great  importance. 

A  great  number  of  most  complete  analyses  of  steel  are 
required  to  settle  this  and  many  other  important  points  in 
the  chemistry  of  this  material,  which  is  daily  growing  in 
importance,  and  with  respect  to  which  new  theories  are  con 
tinually  propounded ;  at  one  time  nitrogen  being  regarded 
as  an  all-important  element,  at  another  titanium,  every 
theory  being  apparently  supported  by  a  number  of  chemical 
analyses  and  determinations  of  tensile  strength,  too  often 
undertaken  in  the  interest  of  the  theory  rather  than  in  the 
unprejudiced  search  after  the  truth. 

Heatorts  Process  for  the  Conversion  of  Cast  Iron  into  Steel 
is  founded  upon  the  action  of  nitrate  of  soda  upon  the 
melted  metal.  The  converter  is  a  cylindrical  vessel  of 
wrought  iron  lined  with  fire-brick,  and  made  to  go  upon 
wheels  so  that  it  may  be  easily  run  under  a  hood  and 
chimney  which  fit  over  it  and  are  attached  to  it  by 


90         Metals :  their  Properties  and  Treatment. 

clamps  during  the  conversion.  At  the  bottom  of  the  con 
verter  there  is  a  cavity  into  which  nitrate  of  soda  is  rammed, 
to  the  amount  of  one-tenth  of  the  weight  of  the  iron  to  be 
converted,  and  covered  with  a  perforated  plate  of  cast  iron. 
The  cast  iron  having  been  melted  in  a  separate  furnace,  is 
run  into  the  converter  through  an  opening  at  the  side  which 
is  then  closed  by  an  iron  plate.  The  high  temperature  of 
the  molten  metal  decomposes  the  nitrate  of  soda,  causing  it 
to  give  off  nitrogen  and  oxygen  gases,  the  latter  acting  upon 
the  carbon  and  silicon  of  the  cast  iron  as  in  the  Bessemer 
process  ;  but,  since  the  proportion  of  oxygen  to  nitrogen  is, 
in  this  case,  nearly  ten  times  as  great  as  in  atmospheric  air, 
the  action  is  far  more  intense,  and  the  conversion  of  a  charge 
of  15  cwt.  is  completed  in  less  than  5  minutes.  The  per 
forated  plate  of  cast  iron  melts  and  mingles  with  the  rest  of 
the  metal.  Notwithstanding  the  larger  proportion  of  oxygen 
in  the  gas  which  passes  through  the  metal,  the  steel  is  not 
sufficiently  liquefied  to  be  poured  out  at  the  conclusion  of 
the  process,  but  is  emptied  out  of  the  converter  in  a  pasty 
state,  and  treated  like  the  blooms  taken  from  the  puddling- 
furnace.  It  has  been  claimed  for  this  process,  that  it  con 
sumes  less  of  the  iron  than  Bessemer's  process,  and  that  the 
removal  of  the  sulphur  and  phosphorus  from  the  cast  iron  is 
assisted  by  the  action  of  the  soda  derived  from  the  nitrate, 
so  that  a  good  bar  iron  or  steel  may  be  produced  from  the 
less  expensive  descriptions  of  cast  iron  which  would  not 
yield  good  results  when  treated  by  Bessemer's  method. 

Nitrate  of  soda  is  imported  in  arge  quantities  from  Chili 
and  Peru,  where  it  occurs  as  an  abundant  natural  product, 
so  that  its  cost  would  probably  not  form  a  serious  obstacle 
to  the  general  introduction  of  the  Heaton  process  if  the 
advantages  which  are  claimed  for  it  can  be  fully  realised. 

Homogeneous  Iron  employed  for  armour-plates  and  cannon, 
which  has  been  already  alluded  to  as  a  mild  steel,  is  manu 
factured  by  a  process  which  consists  in  melting  a  pure 
description  of  bar  iron  (Swedish  iron  being  preferred)  with 


Siemens'  Cast  Steel.  91 

less  than  one  per  cent,  of  charcoal,  in  the  crucibles  em 
ployed  for  the  manufacture  of  cast  steel. 

Siemens  devised  a  process  for  the  production  of  steel  by 
allowing  masses  of  malleable  iron,  directly  they  are  reduced 
from  the  ore,  to  dissolve  in  a  bath  of  melted  pig  iron  heated 


FIG.  28. — Furnace  proposed  by  Siemens,  for  making  cast  steel  in  his  Re 
generative  Furnace.     Beneath  are  shown  the  chambers  containing  fire 
brick  for  accumulating  the  heat  of  the  products  of  combustion  before 
they  pass  into  the  chimney.     B,  Blast-pipe,  from  which  pipes  descend  at     ' 
right  angles  into  the  small  blast-furnaces  A. 

in  the  hearth  or  combustion-chamber  of  the  regenerative  gas- 
furnace.  For  this  purpose,  a  small  blast-furnace  (A,  Fig.  28) 
is  constructed  above  the  combustion-chamber,  so  that  its 
lower  opening  may  rest  in  the  cast  iron  melted  in  the  latter ; 
this  blast-furnace  being  fed  with  haematite  ore  and  small 
coke,  produces  spongy  masses  of  malleable  iron,  which  do 


92         Metals :  their  Properties  and  Treatment. 

not  combine  with  the  carbon  to  form  cast  iron  as  in  the 
ordinary  blast-furnace,  because  the  temperature  is  much 
lower  on  account  of  the  limited  dimensions  of  the  furnace. 
These  spongy  masses  of  iron  are  speedily  dissolved  by  the 
cast  iron,  and  the  proportion  of  iron  to  carbon  becomes 
raised  by  degrees  to  that  necessary  to  constitute  steel,  which 
is  retained  in  the  liquid  state  by  the  very  high  temperature 
which  the  regenerative  or  accumulative  principle  of  the 
Siemens'  furnace  renders  easy  of  attainment. 

Puddled  steel  is  an  inferior  description,  employed  by  boiler- 
makers  and  ship-builders,  and  obtained,  as  its  name  implies, 
by  arresting  the  puddling  process  when  there  is  still  enough 
carbon  (from  five  to  ten  parts  in  a  thousand)  left  to  con 
stitute  a  low  steel,  when  the  damper  is  shut,  and  the  puddled 
balls  treated  as  in  the  case  of  iron. 

To  produce  this  material,  small  charges,  sometimes  only 
2  cwt.,  are  puddled,  and  in  bringing  the  iron  to  nature,  the 
flame  of  the  fire  is  supplied  with  less  air  than  when  fibrous 
bar  iron  is  being  manufactured,  so  that  less  of  the  carbon 
may  be  extracted.  The  presence  of  manganese  in  the  iron 
to  be  puddled  is  decidedly  favourable  to  the  production  of 
puddled  steel,  perhaps  because  the  slags  containing  this 
metal  are  more  thinly  liquid,  and  cover  the  surface  of  the 
iron  more  effectually,  thus  hindering  the  complete  removal 
of  the  carbon. 

By  refining  a  white  cast  iron  containing  manganese  in  a 
forge  constructed  on  the  same  principle  as  the  English 
refinery  hearth  (page  50),  natural  steel  or  German  steel  is 
obtained.  The  spathic  ores  containing  manganese  yield  an 
iron  especially  adapted  for  conversion  into  natural  steel, 
for  which  reason  such  ores  are  sometimes  designated  '  steel 
ores.' 

There  is  as  much  difference  of  opinion  respecting  the 
effect  of  the  presence  of  foreign  matters  upon  steel  as  in  the 


Impurities  in  Steel.  93 

case  of  bar  iron,  and  for  similar  reasons,  namely,  that  the 
quality  of  steel  is  so  much  affected  by  variations  in  the 
mechanical  treatment  to  which  it  is  subjected,  that  it  is 
difficult  to  ascertain  whether  a  particular  defect  in  the  steel 
is  due  to  these  variations  or  to  the  presence  of  such  sub 
stances  as  silicon,  sulphur  and  phosphorus,  which  are  seldom 
exactly  estimated  in  the  analysis  of  steel  by  persons  whom 
practical  experience  has  enabled  to  decide  upon  the  quality 
of  the  metal.  It  is  generally  allowed  that  these  three 
elements  are  injurious  to  steel,  but  it  is  undecided  what 
proportion  of  each  may  be  present  without  serious  dete 
rioration. 

There  appears  to  be  little  question  that  steel  containing 
five  parts  of  silicon  in  a  thousand  does  not  admit  of  being 
forged. 

Sulphur  confers  red-shortness  upon  steel  as  it  does  upon 
bar  iron,  but  the  former  appears  to  suffer  less  injury  than 
the  latter  from  the  presence  of  a  given  proportion  of  sulphur. 
Steel  containing  more  than  two  parts  of  sulphur  in  a  thou 
sand  is  decidedly  brittle  at  a  red  heat,  so  that  it  is  useless 
for  forging  and  can  only  be  employed  for  castings,  for  which 
purpose  it  is  adapted  by  its  increased  fluidity  when  melted. 
Red-short  steel,  like  iron  having  the  same  defect,  appears 
tougher  than  other  qualities  of  steel,  except  at  an  elevated 
temperature.  Manganese  is  believed  to  counteract,  to  a 
great  extent,  the  red-shortness  caused  by  the  presence  of 
sulphur  in  steel. 

How  much  phosphorus  can  be  tolerated  in  steel  has  been 
made  the  subject  of  much  discussion.  It  is  said  that  steel 
manufacturers  object  to  bar  iron  as  a  material  for  converting 
into  steel  when  it  contains  even  one  part  of  phosphorus  in  a 
thousand. 

It  is  alleged  by  some  that  steel  made  from  ores  containing 
titanium  is  superior  in  quality,  but  no  conclusive  evidence 
has  yet  been  adduced  to  show  that  titanium  is  really  bene 
ficial  in  its  effect  upon  steel. 


94         Metals :  their  Properties  and  Treatment. 

A  ready  test  for  distinguishing  between  steel  and  wrought 
iron  consists  in  placing  a  drop  of  diluted  nitric  acid  (aqua 
fortis)  upon  a  clean  surface  of  the  metal,  when  a  greenish- 
grey  stain  appears  upon  the  iron,  whilst  the  steel  exhibits  a 
black  spot  due  to  the  separation  of  carbon. 

Hardening,  Tempering  and  Annealing  Steel. — When  the 
forging  of  steel  implements  is  completed,  they  are  nearly  as 
soft  and  inelastic  as  malleable  iron,  and  their  usefulness 
depends  greatly  upon  the  skill  and  judgment  with  which  the 
subsequent  operations  upon  them  are  conducted.  The  soft 
steel  is  converted  into  hard  steel  by  being  plunged,  when 
red-hot,  into  water,  or  sometimes  into  oil.  After  this  process 
of  hardening,  the  steel  is  found  to  have  increased  slightly 
(about  one-fiftieth)  in  volume,  and  whereas  a  part  of  the  car 
bon  in  the  soft  steel  appears  to  exist  in  an  uncombined  form, 
and  is  left  undissolved  when  the  metal  is  acted  on  by  acids, 
the  whole  of  the  carbon  in  the  hard  steel  is  in  a  state  of 
combination,  so  that  the  effect  of  chilling  upon  soft  steel, 
in  converting  it  into  hard  steel,  is  analogous  to  that  upon 
grey  cast  iron  in  converting  it  into  white  iron. 

The  hardened  steel  is  very  brittle,  and  not  unfrequently 
cracks  spontaneously  like  unannealed  glass.  A  partial  ex 
planation  of  this  is  afforded  by  the  increase  of  volume  which 
attends  the  hardening,  for  when  the  outer  layer  of  particles 
is  chilled,  those  beneath,  which  are  still  in  a  soft  state,  and 
comparatively  free  to  move,  are  restrained  from  expanding 
to  the  proper  volume  of  hardened  steel,  and  the  mass  is  in  a 
state  of  unnatural  strain  or  tension.  Steel  which  has  been 
hardened  in  oil  instead  of  water,  is  tougher  and  less  brittle, 
which  may  perhaps  be  accounted  for  by  the  lower  specific 
heat  of  oil,  in  consequence  of  which  it  abstracts  heat  less 
rapidly  from  the  steel,  and  allows  more  time  for  the  particles 
to  acquire  their  proper  position  in  the  mass.  It  is  some 
times  preferred  to  heat  the  oil  to  about  the  boiling-point  of 
water  before  immersing  the  red-hot  steel,  in  order  that  the 
cooling  may  be  still  less  sudden.  Saws  are  always  hardened 


Hardening  of  Steel.  95 

in  oil,  for  if  water  be  employed  they  become  bent  and 
twisted. 

If  hardened  steel  be  again  heated  and  allowed  to  cool 
slowly,  so  that. there  may  be  less  difference  between  the 
rates  of  cooling  of  the  inside  and  the  outside  of  the  mass, 
the  tension  or  strain  of  its  particles  is  reduced,  and  it 
becomes  far  less  brittle.  In  the  case  of  a  large  casting  such 
as  those  made  by  Krupp,  the  chilling  effect  of  the  air  alone 
would  suffice  to  render  the  steel  too  brittle  to  be  forged,  and 
it  is  found  necessary  to  delay  the  cooling  of  the  outside  of 
the  mass  by  keeping  it  surrounded  with  hot  cinders,  so  that 
a  casting  of  sixteen  tons  will  require  about  three  months  to 
cool  down. 

The  following  results,  quoted  from  Kirkaldy's  'Experi 
ments  on  Wrought  Iron  and  Steel/  illustrate  in  a  very 
striking  manner  the  effect  of  different  modes  of  cooling  upon 
the  tensile  strength  of  steel,  the  bars  being  fixed  at  one 
extremity  and  stretched  by  the  action  of  a  weighted  lever 
attached  to  the  other,  until  they  snapped. 


ns    *        Elongation  Character  of 

per  square  inch        Per  cent'  fracture 

1.  Highly  heated  and  ) 

cooled  in  wafer     \  Entirely  granular 

2.  Highly  heated  and  j 

cooled  slmvly         \  ^  Entirely  fibrous 

3.  Moderately  heated  j  Urd  granular ; 

and  cooled  in  oil  \  4*       j      |rds  fibrous 

4.  Highly  heated  and  j  g  j  Almost  entirely 

cooled  in  oil          \  *       |      granular 

From  these  experiments  (which  are  corroborated  by  others), 
it  appears  that  the  tensile  strength  of  steel  hardened  in 
water,  approaches  most  nearly  to  that  of  the  best  bar  iron, 
although  its  fracture  is  so  widely  different,  while  that  which 
has  been  hardened  in  oil  exhibits  the  highest  tensile  strength, 
with  a  fracture  scarcely  differing  from  that  of  the  weakest 
sample,  although  it  supported  a  breaking  weight  of  nearly 
twice  the  amount. 


96         Metals  :  their  Properties  and  Treatment. 

The  relation  between  ductility  and  fibrous  structure  is 
also  well  exhibited  here  ;  for  the  bar  which  stretched  -f^  ths 
of  its  original  length  before  breaking  was  entirely  fibrous  in 
its  fracture,  whilst  that  which  stretched  only  -fids  of  that 
amount  was  only  frds  fibrous,  and  that  which  did  not 
stretch  at  all  showed  no  fibre  whatever. 

In  proportion  as  the  hardness  of  the  steel  is  reduced  by 
this  process  of  annealing  or  tempering,  its  flexibility  is  in 
creased,  which  allows  of  the  production  of  steel  implements 
of  various  degrees  of  flexibility  adapted  to  their  different 
uses.  If  a  knife-blade,  for  example,  be  made  red-hot,  it  will 
be  found,  after  cooling,  capable  of  being  easily  and  perma 
nently  bent,  as  if  it  were  made  of  wrought  iron  ;  its  temper 
is  then  said  to  be  spoilt,  so  that  a  careful  regulation  of  the 
temperature  is  required  in  letting  the  hardened  steel  down 
to  the  proper  temper.  Few  processes  are  conducted  less 
according  to  definite  rules  than  the  tempering  of  steel,  the 
experience  of  the  workmen  being  more  relied  upon.  In 
some  cases  the  steel  implements,  having  been  raised  to  a 
certain  tempering-heat,  are  allowed  to  cool  in  air,  or  more 
slowly,  in  sand  or  charcoal-powder  ;  in  others,  the  workman 
fixes  or  clinches  the  temper  by  chilling  in  water  as  soon  as  the 
proper  degree  of  softness  has  been  attained.  In  every  case 
it  is  important  that  the  steel  be  raised  to  a  definite  degree 
of  heat  before  the  cooling  process  is  commenced.  A  very 
general  method  of  fixing  this  temperature  is  to  watch  the 
colour  which  a  portion  of  the  steel,  polished  for  the  purpose, 
assumes,  in  consequence  of  the  formation  of  a  very  thin 
film  of  oxide  of  iron  upon  its  surface,  by  the  action  of  the 
oxygen  of  the  air.  The  oxide  which  forms  upon  the  surface 
of  heated  steel,  is  really  an  opaque  black  substance,  but  very 
thin  films  of  it  are  capable  of  decomposing  light  so  as  to 
exhibit  a  colour  varying  with  their  thickness,  exactly  as  the 
film  composing  a  soap-bubble,  though  really  colourless,  ex 
hibits  colours  variegated  according  to  the  thickness  of  its 
different  parts. 


Tempering  of  Steel  97 

Thus,  when  steel  is  heated  to  about  430°  R,  an  extremely 
thin  film  of  oxide  of  iron  is  formed  upon  its  surface,  causing 
it  to  assume  a  faint  yellow  colour;  at  about  450°  the  film 
is  slightly  thicker,  and  shows  a  pale  straw  yellow  ;  a  full 
yellow  colour  appears  at  about  470°,  becoming  a  brown 
yellow  at  490°,  which  becomes  brown,  variegated  with  purple 
spots,  at  510°;  when  the  temperature  has  reached  530°,  the 
entire  surface  has  become  purple,  which  gives  place  to  a 
bright  blue  at  550°,  a  full  blue  at  560°,  and  a  very  dark  blue 
at  600° ;  after  which  the  film  of  oxide  of  iron  becomes  so 
thick  as  to  absorb  all  the  light  which  falls  upon  it  and  to 
appear  black. 

Lancets,  which  must  be  very  hard  in  order  that  they  may 
be  ground  to  a  keen  edge,  are  tempered  to  the  faint  yellow 
tinge,  whilst  razors  and  surgical  knives,  which  must  be 
less  easily  broken,  are  tempered  to  the  straw  yellow.  Pen 
knives  are  tempered  upon  an  iron  plate  over  the  fire,  the 
blades  being  laid  upon  it  on  their  backs  until  they  have 
acquired  the  full  yellow  colour.  Cold  chisels  and  large 
shears  for  cutting  iron  must  stand  rougher  usage,  and  are 
therefore  tempered  to  a  brown  yellow,  whilst  the  brown  with 
purple  spots  marks  the  tempering  heat  for  axes  and  plane- 
irons.  Table  knives  are  heated  till  they  acquire  a  purple 
colour  in  order  to  let  them  down  to  the  proper  temper,  and 
articles  in  which  great  elasticity  is  required,  such  as  swords 
and  watch-springs,  are  tempered  to  a  bright  blue,  while  saws 
are  brought  to  the  highest  tempering  heat,  at  which  the  dark 
blue  colour  shows  itself.  This  temperature,  of  about  600°  F., 
is  that  at  which  oil  boils  and  inflames,  so  that  a  bath  of  oil 
is  very  frequently  used  in  tempering,  the  articles  being  im 
mersed  in  it,  and  the  temperature  ascertained  either  by  a 
thermometer,  or  by  the  volume  and  colour  of  the  smoke 
which  rises  from  the  oil.  Some  tools  are  annealed  by 
plunging  them  into  oil  heated  to  400°  R  and  allowing  them 
to  cool  down  in  it.  Small  steel  tools,  after  being  hardened 
by  chilling  in  water,  are  coated  with  tallow,  heated  over  a 

H 


98         Metals :  their  Properties  and  Treatment. 

flame  till  the  tallow  begins  to  smoke,  and  then  stuck  into 
cold  tallow.  Large  steel  implements  are  let  down  to  the 
proper  temper  by  being  heated  in  a  kind  of  oven  known  as 
a  muffle. 

In  the  subsequent  processes  of  grinding  and  polishing, 
the  tempering  colours  of  steel  articles  are  removed,  but  they 
may  be  seen  in  watch-springs,  which  are  not  so  treated. 
Transparent  varnishes  of  various  colours  are  sometimes 
employed  to  protect  axes,  &c.,  from  rust,  and  have  much  the 
appearance  of  the  tempering  colours.  Steel  articles  are 
sometimes  blued,  to  protect  them  from  rust,  by  heating  them, 
in  a  sand-bath  until  a  blue  film  of  oxide  is  formed. 

The  following  table,  compiled  from  Kirkaldy's  experi 
ments,  before  referred  to,  affords  excellent  illustrations  of 
the  foregoing  statements  with  respect  to  the  hardening  and 
tempering  of  steel : — 

Cast  steel  for  chisels 

Highly  heated  and  cooled  in  water 
Same,  tempered  to  yellow     . 

blue 

Moderately  heated  and  cooled  slowly 
Highly  heated  and  cooled  in  ashes 
Low  heat  and  cooled  slowly  . 

in  coal  tar 

in  tallow 

in  oil 
Moderate  heat  and  cooled  in  coal  tar 

in  tallow 

in  oil 
Highly  heated  and  cooled  in  oil     . 

Case-hardening*. — This  very  useful  process  is  employed 
to  convert  into  steel  the  external  layer  of  particles  of  imple 
ments  made  of  wrought  iron,  in  order  that  they  may  have 
sufficient  hardness  to  resist  friction,  possessing  at  the  same 
time  the  toughness  of  malleable  iron.  Keys  and  gun-locks 


Tensile  strength 
(toughness) 
in  tons 
per  square  inch 

Elongation 
per  cent, 
(flexibility) 

40 

O 

45 

o 

5° 

of 

53 

71 

54 

7 

56 

10 

631 

8! 

64! 

7 

73 

5 

74} 

6 

79^ 

2| 

821 

2| 

96 

31 

-  *  This  term  is  sometimes  erroneously  applied  to  designate  the  opera 
tion  of  hardening  cast-iron  or  steel  by  chilling  in  water. 


Case-hardening.  99 

are  among  the  articles  which  are  so  treated.  The  operation, 
as  sometimes  performed,  is  an  imitation,  on  the  small  scale, 
of  the  process  of  cementation,  for  it  consists  in  burying  the 
wrought  iron  implement  in  some  carbonaceous  substance, 
and  raising  it  to  a  red  heat,  when  the  outer  layer  of  particles 
acquires  enough  carbon  to  convert  it  into  steel.  All  car 
bonaceous  substances  are  not  equally  efficacious  for  case- 
hardening  ;  wood  charcoal  does  not  answer  so  well  as  that 
obtained  from  bone  or  horn;  and  in  some  of  the  old  pre 
scriptions  urine  is  an  important  ingredient.  It  is  an  in 
teresting  fact  that  the  substance  which  has  of  late  years  been 
found  the  most  convenient  and  effectual  for  case-hardening 
is  the  yellow  prussiate  of  potash,  a  salt  in  the  preparation  of 
which  bone,  horn,  and  similar  animal  substances  are  indis 
pensable,  the  carbon  which  they  contain  passing  into  a  new 
form  of  combination  in  the  salt,  whence  it  is  transferred  to 
the  iron  undergoing  case-hardening.  The  implement  to  be 
case-hardened  is  heated  to  bright  redness,  and  sprinkled 
with  the  finely-powdered  prussiate  of  potash,  and  as  soon  as 
this  has  been  decomposed  by  the  heat,  the  metal  is  quenched 
in  water. 

The  circumstance  that  those  substances  are  found  to  be 
preferable  for  case-hardening  which  contain  nitrogen  as  well 
as  carbon,  has  led  many  to  believe  that  the  former  element 
plays  an  important  part  in  the  production  of  steel,  and 
attempts  have  been  made  by  chemists  to  show  that  nitrogen 
is,  like  carbon,  an  essential  constituent  of  steel ;  their  success 
has  not,  however,  been  so  complete  as  to  induce  the  general 
acceptance  of  a  new  explanation  of  the  conversion  of  iron 
into  steel. 

Malleable  Cast  Iron.—1\\vs>  term  is  applied  to  the  result 
of  a  process  which  is  just  the  reverse  of  case-hardening,  for 
it  consists  in  Removing  the  carbon,  or  a  large  proportion 
of  it,  from  articles  made  of  cast  iron,  so  as  to  confer  upon 
them  the  toughness  of  malleable  iron.  It  is  practised  in  the 
c^ase  of  small  articles,  such  as  buckles,  which  have  to  be 


H  2 


I  oo       Metals :  their  Properties  and  Treatment. 

produced  in  great  numbers  at  a  low  price.  These  are  made 
from  a  superior  quality  of  cast  iron,  usually  from  that  which 
has  been  smelted  with  charcoal,  and  are  then  de-carburetted 
by  being  imbedded  in  some  substance  capable  of  imparting 
oxygen  to  the  carbon  at  a  red  heat,  and  removing  it  in  the 
form  of  carbonic  acid  gas.  Powdered  haematite  iron  ore 
(peroxide  of  iron)  is  sometimes  employed,  and  sometimes 
the  iron  scale  or  black  oxide  which  is  detached  in  the 
process  of  forging  bar  iron.  Manganese  ore  (peroxide  of 
manganese)  also  answers  the  purpose. 

Extraction  of  Malleable  Iron  directly  from  the  Ore. — The 
modern  method  of  smelting  iron  ores  in  the  blast-furnace, 
so  as  to  obtain  cast  iron,  which  is  converted  by  subsequent 
processes  into  malleable  iron,  owes  its  origin  to  the  necessity 
created  by  the  great  demand  for  that  metal,  of  extracting  it 
from  the  poorer  ores,  such  as  clay  ironstone,  which  could 
not  be  made  to  yield  their  iron  by  a  more  direct  process. 
In  the  early  history  of  the  metallurgy  of  iron,  there  is  no 
mention  of  cast  iron,  the  intermediate  product  of  the  modern 
iron  smelting,  the  metal  being  obtained  at  once  in  a  mal 
leable  condition  by  a  process  which  is  still  practised,  under 
various  modifications,  in  districts  where  ores  composed  of 
nearly  pure  oxide  or  carbonate  of  iron  can  be  obtained, 
together  with  a  sufficient  supply  of  the  charcoal  which  is 
necessary  for  the  operation. 

The  direct  process  of  extracting  malleable  iron  is  com 
monly  spoken  of  as  the  Catalan  process,  since  it  has  been 
practised  from  a  very  remote  period  in  the  Spanish  province 
of  Catalonia,  where  the  magnetic  iron  ore  and  haematite  of 
the  Pyrenees  are  smelted  with  the  charcoal  supplied  by  the 
surrounding  forests.  The  smelting  works  comprise  a  forge, 
a  blowing  machine,  and  a  hammer,  but  the  first  alone  will 
be  here  described  in  order  to  illustrate  this  method  of  treat 
ing  iron  ores. 

The  crucible  or  hearth  is  a  nearly  rectangular  trough  (M, 
Fig.  29)  well  built  around  with  masonry,  about  17  inches 


Direct  extraction  of  Wrought' J 


101 


•Mm 


deep,  21  inches  long,  and  18^  inches  wide,.  '/The  i)6tte>m'  btf 
the  crucible  is  composed  of  a  block  of  granite,  which  is  sup 
ported  upon  small  arches  to  keep  it  dry. 

That  side  of  the  hearth  at  which  the  blast  from  the  tuyere 
(T)  enters  is  perpendicular,  being  built  up  of  massive  pieces  of 
iron  (/),  the  blast-pipe,  or  tuyere,  of  copper,  being  supported 
upon  the  uppermost  piece  in  such  a  manner  that  its  inclina 
tion  to  the  bottom  of  the  crucible  can  be  varied  at  pleasure, 
since  this  appears  to 
exercise  much  influ 
ence  upon  the  suc 
cess  of  the  operation. 
The  wall  opposite  to 
the  blast  is  built  up  of 
wedge-shaped  pieces 
of  iron  (s)  and  pre 
sents  a  curved  sur 
face.  The  working  tj 
side  of  the  hearth  is 
composed  of  three 
thick  pieces  of  iron 
placed  end  to  end, 
the  side  opposite  to 
it  being  lined  with 
fire-clay,  and  having 
a  moderate  inclina 
tion. 

To  begin  the  ope 
ration  of  smelting,  the  hearth  is  about  half  filled  with  burn 
ing  charcoal,  and  a  shovel  is  held  so  as  to  divide  the 
space  above  the  fuel  into  two  unequal  compartments, 
the  larger  one,  next  to  the  blast-pipe,  being  filled  with 
charcoal,  whilst  the  other,  about  half  its  size,  is  charged 
with  the  ore,  previously  calcined,  broken  into  small  pieces 
and  sifted  from  the  dust ;  the  ore  is  piled  up  in  a  ridge  (/) 
upon  the  side  (g)  of  the  hearth,  so  that  it  may  be  raked  into 


FIG.  29. — Catalan  Forge. 


IO2       M'eiitls :  their  Properties  and  Treatment. 

(tKe  five'  as  the  cha~gf;  sinks  down.  The  shovel  forming  the 
temporary  partition  having  been  withdrawn,  the  blast  is 
gradually  applied  so  that  it  may  attain  its  full  force  after 
about  two  hours,  the  fuel  and  ore  being  continually  pressed 
down  into  the  hearth  by  the  labourers.  One  portion  of  the 
oxide  of  iron  is  reduced  to  the  metallic  state  by  the  carbonic 
oxide  formed  from  the  carbon  of  the  charcoal  and  the 
oxygen  of  the  air-blast  (see  page  31),  but  the  metallic  iron 
thus  produced  is  not  exposed  to  a  sufficiently  high  tem 
perature  to  enable  it  to  acquire  enough  carbon  for  its  con 
version  into  cast  iron,  and  it  is  obtained  in  the  form  of 
spongy  masses  of  malleable  iron  or  steely  iron,  according 
to  the  proportion  of  carbon  taken  up  by  the  metal.  This 
depends,  to  a  great  extent,  upon  the  manner  in  which  the 
operation  is  conducted.  If  the  si/tings  from  the  broken  ore, 
moistened  with  water  to  prevent  their  dispersion,  be  added 
to  the  charge  in  large  proportion,  the  iron  contains  less 
carbon  and  is  less  steely  than  when  these  are  employed  in 
smaller  quantity,  probably  because  the  oxidising  action  which 
they  exert  at  a  high  temperature  is  unfavourable  to  the 
acquisition  of  carbon  by  the  metal.  The  iron  is  also  less 
steely  when  the  blast  is  directed  down  to  the  bottom  of  the 
hearth,  so  that  it  is  less  exposed,  as  it  separates  from  the 
ore,  to  the  action  of  unburnt  gases  very  rich  in  carbon. 

A  large  proportion  of  the  oxide  of  iron  escapes  reduction, 
and  combines  with  the  silica  contained  in  the  ore  and  fuel, 
to  form  a  very  fusible  silicate  of  iron,  the  bulk  of  which  is 
run  off  through  an  opening  at  the  bottom  of  the  crucible. 

In  about  five  or  six  hours,  enough  ore  is  reduced  to  furnish 
two  or  three  hundredweight  of  metal,  in  lumps  which  are 
welded  together  by  pressing  them  with  an  iron  rod,  on  the 
end  of  which  they  are  transported  to  the  hammer,  where 
they  are  stamped  into  a  compact  state,  and  afterwards  forged 
into  bars. 

The  iron  thus  obtained  is  usually  of  excellent  quality,  not 
having  become  contaminated  with  foreign  matters  to  the 


Native  Copper.  103 

same  extent  as  the  melted  pig  iron  from  the  blast  furnace ; 
but  the  processes  a  very  extravagant  one,  the  ore  being 
made  to  yield  no  more  than  one-third  of  its  weight  of  metal, 
with  a  consumption  of  more  than  its  own  weight  of  charcoal. 

The  experiments  of  Kirkaldy  have  shown  that  the  quality 
of  iron  and  steel  is  pretty  correctly  indicated  by  their  specific 
gravities,  the  specific  gravity  of  rolled  steel  bars  being  found 
to  range  between  7'8303  and  7-6698;  that  of  rolled  iron 
bars,  between  77652  and  7-2898,  the  best  qualities  having 
the  highest  specific  gravities. 


COPPER. 

The  use  of  metallic  copper  dates  from  an  earlier  period 
than  that  of  iron,  although  the  former  metal  is  by  no  means 
so  plentifully  diffused  over  the  earth's  surface  as  the  latter. 
Copper,  however,  is  of  much  more  frequent  occurrence  in 
the  pure  metallic  state,  and  some  of  the  ores  of  copper  can 
be  much  more  easily  made  to  yield  their  metal  in  a  mal 
leable  condition. 

Native  Copper  is  sometimes  found  in  masses  of  large  size, 
having  a  very  curious  branch-like  appearance,  each  branch 
being  composed  of  crystals  of  copper,  somewhat  deformed, 
united  together.  Such  masses  have  been  obtained  from  the 
southern  shore  of  Lake  Superior.  Some  of  the  blocks  weigh 
as  much  as  400  tons,  and  since  the  toughness  of  the  metal 
prevents  it  from  being  blasted  with  gunpowder,  much  time 
and  labour  are  expended  in  cutting  the  blocks  into  portable 
masses  with  steel  chisels.  Metallic  copper  is  also  found  in 
veins  disseminated  in  granite,  in  Cornwall  and  North  Wales, 
and  in  many  other  parts  of  the  world.  A  very  remarkable 
form  of  native  copper  is  the  copper  sand  or  copper  barilla 


104       Metals:  their  Properties  and  Treatment. 

of  Chili,  which  consists  of  grains  of  metallic  copper  mixed 
with  quartz.  Native  copper,  especially  that  from  Lake 
Superior,  is  of  a  very  pure  description,  and  is  tougher  than 
any  but  the  best  specimens  of  the  copper  extracted  from 
the  ores. 

The  following  table  exhibits  the  composition  of  the  ores 
of  copper  : — 

Ores  of  Copper. 

Composition 
Copper,  Oxygen 


Red  Copper  Ore 
Black  Oxide 
Copper  Glance 
Indigo  Copper 
Copper  Pyrites 
Peacock  Copper 

Grey  Copper  Ore 

Malachite 
Blue  Malachite 


Copper,  Oxygen 
Copper,  Sulphur 
Copper,  Sulphur 
Copper,  Iron,  Sulphur 
Copper,  Iron,  Sulphur 
j  Copper,  Iron,  Sulphur, 
|  Antimony,  Arsenic 
j  Copper,  Oxygen, 
\  Carbonic  Acid,  Water 
j  Copper,  Oxygen, 
(  Carbonic  Acid,  Water 


Copper  in  100  parts 
of  pure  ore 
89 
80 
80 
67    ' 

II 

Variable 

58 
55 


Copper  Pyrites  or  Yellow  Copper  Ore  is  the  most  abundant 
English  ore  of  copper,  being  found  in  large  quantities  in 
Cornwall  and  Devon.  It  is  also  plentiful  in  Sweden, 
Saxony,  Siberia,  and  Australia.  The  colour  of  pure  copper 
pyrites  is  a  fine  brass  yellow,  but  some  specimens  are  much 
paler,  from  the  presence  of  iron  pyrites.  Copper  pyrites  is 
much  softer  than  iron  pyrites,  and  the  richness  of  a  sample 
may  be  in  some  measure  inferred  from  this  character. 
Although  detached  specimens  of  pure  copper  pyrites  may 
be  easily  procured,  it  is  always  associated,  in  the  vein,  not 
only  with  the  vein-stone  or  gangue^  generally  composed  of 
quartz  (silica)  or  fluor  spar  (fluoride  of  calcium),  but  with 
arsenical  pyrites  (composed  of  arsenic,  iron,  and  sulphur)  and 
tinstone  (oxide  of  tin). 

Peacock  Ore  or  Variegated  Copper  Ore  is  found  at  St. 
Austle  and  Killarney.  Like  copper  pyrites,  it  is  composed 
of  copper,  iron,  and  sulphur,  but  it  contains  a  larger  propor 
tion  of  copper  than  that  ore. 


Ores  of  Copper.  105 

Grey  Copper  Ore  is  one  of  the  most  abundant  and  impor 
tant  ores  of  this  metal,  as  well  as  the  most  complex  and 
variable  in  composition.  Like  the  preceding  ores,  it  con 
tains  the  copper  in  chemical  combination  with  sulphur,  but 
this  latter  element  is  also  combined  with  iron,  antimony  and 
arsenic,  and  generally  with  zinc  and  silver.  The  proportion 
of  copper  varies  between  25  and  40  parts  in  the  hundred, 
and  the  silver  is  very  commonly  present  in  sufficient  quan 
tity  to  render  its  extraction  a  matter  of  great  importance. 
Cornwall  and  Freiberg  furnish  large  supplies  of  grey  copper 
ore. 

Copper-glance,  also  a  Cornish  ore  of  great  importance,  is  a 
chemical  compound  of  copper  and  sulphur  which  is  gene 
rally  free  from  any  important  foreign  minerals. 

Indigo  Copper,  so  named  from  its  dark  blue  colour,  is 
found  in  Chili. 

Red  Copper  Ore  differs  from  the  preceding  ores  in  being 
free  from  sulphur,  and  since  it  is  found  pretty  abundantly 
in  Cornwall,  Cuba  and  elsewhere,  it  plays  a  prominent  part 
in  some  of  the  stages  of  the  process  of  copper-smelting. 

Black  Oxide  of  Copper  is  found  in  Chili. 

Malachite  or  Green  Carbonate  of  Copper  is  a  very  fine 
green  ore,  some  specimens  being  so  beautifully  veined  that 
they  are  more  highly  prized  for  ornamental  purposes  than 
as  an  ore  of  copper.  It  is  a  very  pure  and  valuable  ore, 
but  is  not  abundant  in  England,  being  found  chiefly  in 
Siberia,  the  Ural  Mountains  and  Australia. 

Blue  Malachite  or  Azurite  or  Blue  Carbonate  of  Copper 
contains  a  larger  proportion  of  carbonic  acid  than  the  green 
carbonate,  and  is  generally  found  in  the  same  localities. 
The  mines  of  Burra  Burra  in  South  Australia  are  noted  for 
malachite  ores,  which  yield  copper  of  excellent  quality. 

The  Cornish  copper  ores  are  shipped  to  Swansea  in  order 
to  be  smelted,  the  vessels  returning  to  Cornwall  laden  with 
the  coal  required  for  the  tin-works.  The  ores  from  Aus-, 
tralia,  Chili,  Cuba  (Cobre  ores),  &c.,  are  also  received -at 


io6       Metals :  their  Properties  and  Treatment. 

Swansea,  the  neighbourhood  of  which  furnishes  an  abun- 
cjance  of  anthracite  coal. 

Copper  ores  are  also  mined  in  Anglesea,  the  Isle  of  Man, 
Lancashire,,  and  some  parts  of  Ireland  and  Scotland. 

EXTRACTION    OF   COPPER    FROM    ITS    ORES. 

Probably  no  other  metallurgic  operation  presents  such  an 
appearance  of  complexity  as  the  smelting  of  copper  ores, 
but  this  is  due  to  the  great  variety  of  the  ores  to  be  treated, 
which  necessitates  their  introduction  at  different  stages  of 
the  process.  Thus,  a  smelting  process  adapted  for  copper 
pyrites  must  contain  provisions  for  the  removal  of  arsenic 
and  sulphur,  which  are  not  present  in  the  carbonates  and 
the  oxides  of  copper,  so  that  the  processes  of  smelting  are 
arranged  in  such  a  manner  that  these  ores,  as  well  as  the 
slags  obtained  in  some  of  the  operations,  can  be  introduced 
after  the  sulphur  and  arsenic  have  been  expelled. 

In  a  work  like  the  present,  it  is  not  advisable  to  attempt 
a  detailed  account  of  smelting  processes  which  are  subject 
to  frequent  alterations  in  order  to  suit  different  lots  of  ore, 
particularly  when  such  alterations .  result  from  the  applica 
tion  of  practical  experience  on  the  part  of  the  smelter,  and 
do  not  admit  of  clear  explanation  upon  simple  chemical 
principles.  A  general  outline  only  of  the  extraction  of 
copper  from  its  ores  will  be  given  here,  and  before  this  is 
entered  upon,  it  may  assist  the  reader  to  state  that  it  may 
be  summed  up  under  the  following  heads  : 

1.  Roasting  processes,  intended  to  expel  arsenic  and  sul 
phur,  and  to  convert  the  iron  into  oxide  of  iron. 

2.  Melting  processes,  intended  to  remove  the  oxide  of  iron 
by  dissolving  it  with  silica  at  a  high  temperature,  and  to 
obtain  the  copper  as  a  pure  combination  of  copper  with 
sulphur  (sulphide  of  copper). 

3.  Roasting  and  melting,  in  a  single  process,  to  expel  the 
sulphur  and  obtain  metallic  copper. 

Before  being  subjected  to  the  first  process,  the  ores  are 


Copper  smelting  process. 


10; 


broken  into  pieces  of  the  size  of  a  nut,  and  so  assorted  that 
the  lot  to  be  smelted  may  contain  about  eight  or  ten  parts 
of  metallic  copper  in  the  hundred.  Moreover,  as  there  is 
much  gangue  or  earthy  matter  associated  with  the  ores,  they 
are,  if  possible,  so  mixed  that  they  may  serve  as  fluxes  to 
each  other,  by  producing  chemical  compounds  capable  of 
becoming  liquefied  by  the  high  temperature  of  the  furnace. 

T\\efluor*  spar,  which  is  so  commonly  associated  with 
copper  pyrites,  derives  its  name  from  its  power  to  effect  the 
liquefaction  of  earthy  substances.  Fluor  spar  is  composed 


FIG.  30.— Furnace  for  roasting  Copper  Ores.     BB,  Working  doors. 
D,  Vault  for  receiving  the  roasted  ore. 

of  calcium  and  fluorine;  if  it  be  strongly  heated  in  contact 
with  silica  (quartz),  which  consists  of  oxygen  combined  with 
silicon,  the  latter  takes  up  the  fluorine  to  form  fluoride  of 
silicon  gas,  whilst  the  calcium  and  oxygen  unite  to  produce 
lime,  which  combines  with  another  portion  of  the  silica  to 
form  a  silicate  of  lime.  The  silicate  of  lime  would  not  easily 
fuse  into  a  slag  by  itself,  but  when  clay  and  oxide  of  iron  are 
present,  as  is  always  the  case  in  the  melting  furnaces,  a  slag 
is  readily  produced. 

ist  Process  in  Copper-smelting.     Calcining  or  Roasting  to 

*  From  the  Latin  fltto,  to  flow. 


1 08       Metals :  their  Properties  and  Treatment. 

Expel  Arsenic  and  part  of  the  Sulphur. — The  roasting-furnace 
or  caldner  (Figs.  30,  31,  32)  is  a  reverberator y  furnace,  with  a 
hearth  (A)  of  large  size  (about  sixteen  feet  by  fourteen)  to 
allow  of  the  ore  being  spread  out  in  a  thin  layer  upon  it. 
The  hearth  is  commonly  built  of  fire-bricks  set  on  edge  and 
bedded  in  fire-clay,  and  the  flame  is  reverberated  upon  it  by 
an  arch  of  about  two  feet  in  average  height.  At  one  end  of 
the  hearth,  near  the  fire-place,  there  is  an  opening  or  flue  (o) 
through  which  air  may  be  admitted  to  the  hearth,  to  furnish 
the  oxygen  necessary  for  the  chemical  changes  effected  in 
the  roasting  process.  On  each  side  of  the  hearth  there  are 


FIG.  31. — Furnace  for-roasting  Copper  Ores.    Section  through  the  line  x  Y  of 
the  plan  (fig.  32). 

two  openings  (r)  closed  with  iron  doors,  through  which  the 
roasted  ore  is  raked  out  into  the  arch  (u)  beneath  the 
furnace.  The  ore  is  admitted  by  opening  the  hoppers  (T) 
over  the  arch  of  the  furnace,  where  it  is  previously  warmed 
by  the  waste  heat.  The  fuel  employed  in  the  calciners  at 
Swansea  is  anthracite  mixed  with  one-fourth  of  bituminous  or 
caking  coal,  which  is  necessary  to  counteract  the  tendency 
of  anthracite  to  split  up  into  small  pieces  and  choke  the  air- 
passages  of  the  fire,  the  bituminous  coal  being  softened  by 
the  heat,  and  binding  the  anthracite  together.  The  fire  of 
the  calciners  requires  special  management  in  order  that  the 
ore  upon  the  hearth  maybe  brought  to  the  proper  tem- 


Roasting  of  Copper  Ores. 


109 


perature.  Anthracite  coal  is  not  easily  made  to  burn  in  an 
ordinary  grate,  and,  when  burning,  it  raises  the  bars  to  so 
high  a  temperature  that  they  rapidly  oxidise  and  burn  away. 
To  avoid  this,  a  layer  of  clinker  or  fused  ash  from  the  coal 
is  built  up  on  the  bars  of  the  grate  (F)  so  as  to  preserve  them 
from  direct  contact  with  the  glowing  coal,  and  air-passages 
are  made  through  this  layer,  so  that  the  air  becomes  heated 
in  passing  through  them,  before  it  actually  reaches  the  fire, 
the  combustion  of  the  anthracite  being  thus  effected  by  a 
current  of  heated  air.  The  oxygen  of  the  air,  passing  through 


FIG.  32. — Furnace  for  roasting  Copper  Ores.     Plan  at  the  line  z  v  of  the 
section  (fig.  31). 

the  column  of  heated  fuel,  combines  with  the  carbon  to  form 
carbonic  oxide  (see  p.  31),  and  this  gas,  being  highly  heated, 
takes  fire  in  the  air  admitted  on  to  the  hearth  of  the  furnace, 
giving  a  sheet  of  flame  which  is  drawn  through  the  furnace 
by  the  action  of  the  chimney  with  which  the  flues  (R)  com 
municate,  and  raises  the  ore  to  the  temperature  necessary 
for  roasting  it.  Since  the  air  is  heavier  than  the  burning 
gas,  a  layer  of  air  always  exists  beneath  the  latter,  separating 
it  from  the  ore,  thus  preventing  the  ore  from  attaining  its 
melting  point,  and  securing  a  sufficient  supply  of  oxygen. 


no       Metals :  their  Properties  and  Treatment. 

Each  calciner  is  charged  with  three  tons  of  the  broken 
ore,  which  is  spread  evenly  over  the  hearth,  and  roasted  for 
twelve  hours,  being  occasionally  raked  over  through  the 
working-doors  (/)  in  order  to  expose  fresh  portions  to  the 
action  of  the  air,  and  to  prevent  any  part  of  the  ore  from 
being  melted.  At  this  high  temperature,  the  arsenic  present 
in  the  copper  ore  combines  with  oxygen  from  the  air  to  form 
arsenious  acid  (white  arsenic)  which  passes,  in  the  form  of 
vapour,  into  the  flues.  About  half  of  the  sulphui  in  the  ore 
also  combines  with  oxygen  to  form  sulphurous  acid  gas 
which  passes  up  the  chimney,  a  small  quantity  of  sulphuric 
acid  being  also  formed  and  remaining  in  the  ore  as  sulphate 
of  copper. 

Since  iron  exerts  the  greater  chemical  attraction  for  oxy 
gen,  and  copper  for  sulphur,  a  large  proportion  of  iron 
acquires  oxygen  and  becomes  converted  into  the  oxide  of 
iron,  while  a  much  smaller  proportion  of  the  copper  com 
bines  with  the  oxygen  from  the  air  to  form  suboxide  of  copper. 
When  the  gases  and  vapours  issuing  from  the  calciners  are 
allowed  to  escape  directly  into  the  air,  they  form  a  dense 
grey  cloud  of  copper-smoke  which  contains  the  sulphurous 
acid,  mixed  with  a  little  vapour  of  sulphuric  acid,  the 
arsenious  acid,  which  condenses  in  the  air  to  a  fine  powder, 
and  some  hydrofluoric  acid  gas,  produced  from  the  fluor 
spar.  The  injurious  effect  of  these  products  upon  the  health 
and  vegetation  of  the  neighbourhood  has  induced  the  copper 
smelters  to  devise  means  for  condensing  them  by  passing 
them  into  flues  and  condensing  chambers  where  they  are  met 
by  showers  of  water. 

At  some  works  it  has  been  found  profitable  to  convert  the 
sulphurous  acid  into  oil  of  vitriol  instead  of  allowing  it  to 
escape,  but  in  this  case  it  is  necessary  to  prevent  the  pro 
ducts  of  combustion  of  the  fuel  from  mixing  with  the  copper- 
smoke.  Spence's  calciner  employed  for  this  purpose  has  the 
fire  passing  under  the  hearth  instead  of  over  it.  This  furnace 
is  50  feet  long,  and  the  ore  is  gradually  raked  from  the  cooler 


Melting  for  Coarse  Metal.  1 1 1 

to  the  hotter  end  as  it  becomes  less  fusible.  The  waste  heat 
of  an  adjoining  smelting  furnace  is  sometimes  employed  in 
these  calciners,  and  the  calcined  ore  is  raked  at  once  into 
the  smelting  furnace.  In  Gerstenhbffer1  s  furnace  the  ores  are 
crushed  between  rollers,  and  allowed  to  fall  over  rows  of  red 
hot  bricks  in  a  vertical  furnace,  through  which  a  blast  of 
heated  air  is  passed  in  order  to  burn  the  sulphur  into 
sulphurous  acid,  which  is  then  conducted  into  the  leaden 
chambers,  where  it  is  converted  into  oil  of  vitriol. 

2nd  Process  in  Copper-smelting.  Melting  for  Coarse  Metal,  to 
Dissolve  the  Oxide  of  Iron  as  a  Silicate. — It  has  been  seen  that 
the  ist  process  has  had  the  effect  of  converting  a  large  pro 
portion  of  the  sulphuret  of  iron  present  in  the  pyrites  into 
oxide  of  iron,  which  it  is  the  object  of  the  present  process 
to  remove  by  causing  it  to  combine  with  silica,  to  form  a 
compound  capable  of  being  melted  and  separated  from  the 
r.est  of  the  ore.  At  this  stage  the  copper  ores  containing 
silica  (quartz)  can  be  introduced  with  advantage,  provided 
that  they  are  free  from  sulphur.  It  must  not  be  forgotten 
that,  during  the  process  of  calcining,  a  small  proportion  of 
the  sulphuret  of  copper  in  the  pyrites  has  been  converted 
into  an  oxide  of  copper,  which  resembles  the  oxide  of  iron 
in  its  property  of  combining  with  silica  at  a  high  temperature, 
to  form  a  melted  silicate  which  would  pass  away  in  the  slag, 
entailing  a  considerable  loss  "of  copper.  This  is  prevented 
by  the  sulphuret  of  iron  which  is  still  present  in  the  calcined 
ore,  and,  at  the  high  temperature  at  which  the  fusion  is 
effected,  exchanges  constituents  with  the  oxide  of  copper, 
forming  oxide  of  iron  and  sulphuret  of  copper.  The  slag 
from  the  4th  process,  to  be  presently  described,  is  also 
appropriately  introduced  in  this  fusion,  since  it  contains  a 
considerable  quantity  of  oxide  of  copper,  which  exchanges, 
as  above,  with  the  sulphuret  of  iron  in  the  calcined  ore,  fur 
nishing  more  sulphuret  of  copper  to  pass  into  the  coarse 
metal,  and  oxide  of  iron  to  be  removed  in  the  slag.  The 
slag  from  the  4th  process  (called  met  at  slag]  also  furnishes 


112 


Metals :  their  Properties  and  Treatment. 


silica  to  assist  in  removing  the  oxide  of  iron.  In  some  cases, 
the  smelter  adds  some  fluor  spar  in  order  to  facilitate  the 
fusion  of  the  charge. 

The  ore-furnace  (Figs.  33,  34),  as  it  is  called,  in  which  the 
melting  for  coarse  metal  is  effected,  is  also  a  reverberatory 
furnace,  but  its  hearth  (A)  is  much  smaller  than  that  of  the 
calciner  (usually  about  one-third  of  the  size),  because  the 
charge  has  to  be  raised  to  a  much  higher  temperature ;  for 
which  reason,  also,  the  fire-grate  is  larger  in  proportion ;  the 
hearth  is  also  slightly  inclined  on  all  sides  towards  a  depres- 


FIG.  33. — Section  of  Ore-furnace  for  smelting  Copper  Ores.  T,  Hopper  for 
introducing  the  charge,  p,  Tap-hole  for  discharging  the  slag  into  the 
slag-moulds  u.  c,  Flue  leading  to  the  chimney. 

sion  or  cavity  (B)  at  one  side,  which  serves  as  a  crucible  in 
which  the  melted  coarse- metal  collects.  The  fuel  is  a 
mixture  of  anthracite  with  one-third  of  bituminous  coal. 
The  charge  of  this  furnace  is  composed  of  the  following 
materials,  selected  for  the  reasons  above  given,  viz. : — 

Calcined  or  roasted  ore,  usually  about  18  cwt. 

Ores  containing  oxide  of  copper  and  silica,  3  cwt. 

Metal-slag  from  process  4,  containing  oxide  of  iron, 
silica,  and  some  oxide  of  copper,  6  cwt. 

Fluor-spar,  occasionally. 


Melting  for  Coarse  Metal.  1 1 3 

The  slag  is  the  first  to  fuse,  in  about  half-an-hour  after  the 
charge  has  been  introduced,  and  by  degrees  the  whole  of  the 
materials  become  liquid,  and  enter  into  violent  ebullition, 
caused  by  disengagement  of  sulphurous  acid  gas,  produced 
by  a  secondary  decomposition  of  no  importance  from  a 
metallurgic  point  of  view,  save  that  the  ebullition  favours 
the  intimate  mixture  of  the  melted  matters  on  the  hearth. 

After  three  or  four  hours,  the  furnace-man  mixes  up  the 


FIG.  34.— Plan  of  Ore-furnace  for  smelting  Copper  Ores.     F,  The  grate 
R,  Tank  for  granulating  the  coarse  metal. 

melted  matters  with  a  rake,  and  raises  the  temperature  very 
considerably,  to  favour  the  separation  of  the  coarse  metal 
from  the  slag.  In  about  half-an-hour,  the  tap-hole  (b,  Fig. 
34),  which  communicates  with  the  cavity  in  the  hearth,  is 
opened,  and  the  matt*  or  regulus  of  coarse  metal  is  run  out, 
through  an  iron  gutter  (a)  into  an  iron  box  (G,  Fig.  35),  per 
forated  at  the  bottom,  and  standing  in  a  cistern  through 

*  From  the  French  mat,  heavy. 


114      Metals:  their  Properties  and  Treatment. 

which  water  is  constantly  running ;  the  coarse  metal  is  thus 
granulated  or  divided  into  small  irregular  grains,  in  order  to 
fit  it  for  undergoing  the  next  operation. 

Sometimes  the  regulus  from  two  or  three  operations  is 
allowed  to  accumulate  in  the  furnace  before  tapping,  the  slag 
alone  being  raked  out  before  the  introduction  of  a  fresh  charge. 

The  iron  box  containing  the  regulus  is  raised  from  out  of 
the  cistern  by  a  winch  (w),  and  its  contents  are  carried  to 
the  calcining  furnace. 


FIG.  35. — Elevation  of  Ore-furnace  for  smelting  Copper  Ores.  H,  Hopper 
for  introducing  the  charge.  K,  Chimney,  c,  Fire-door,  a,  Pipe  for 
supplying  water  to  the  tank. 

This  coarse  metal  contains  copper,  iron,  and  sulphur  in 
about  the  same  proportion  in  which  they  are  present  in 
pure  copper  pyrites,  so  that  the  copper  amounts  to  about  33 
parts  in  the  hundred,  or  nearly  four  times  the  proportion  con 
tained  in  the  raw  ore  at  the  commencement  of  the  process. 

The  slag  (ore-furnace  slag)  is  raked  out  into  sand-moulds 


t)re-furnace  Slag.  Ir^ 

(u»  Fig-  34),  connected  with  each  other  by  openings  in  their 
sides,  where  it  solidifies  into  blocks  of  a  black,  somewhat 
glassy,  appearance,  interspersed  with  white  fragments  of 
quartz.  It  is  used  for  rough  building  purposes  in  the  neigh 
bourhood  of  the  copper  works.  The  ore-furnace  slag  is 
composed  essentially  of  oxide  of  iron  (ferrous  oxide)  and 
silica  combined  in  about  equal  proportions,  and  would  be 
spoken  of,  in  chemical  language,  as  a  silicate  of  iron  or 
ferrous  silicate.  It  contains  also  a  little  copper,  usually 


FIG.  36. — Copper  Smelting-furnace. 


amounting  to  one  part  in  140  parts,  representing  a  loss  to 
the  smelter  which  appears  unavoidable.  Occasionally,  a 
small  quantity  of  regulus  is  found  at  the  bottom  of  the 
blocks  of  slag,  from  which  it  is  separated  by  hand-picking. 
Fig.  36  exhibits  the  general  arrangements  connected  with 
the  ore-furnace,  and  shows  the  furnace-man  discharging  the 
slag. 


I  2 


Ii6      Metals :  their  Properties  and  Treatment. 

$rd  Process  in  Copper-smelting.  Calcination  of  the  Coarse 
Metal,  to  convert  more  of  the  Sulphur et  of  Iron  into  Oxide. — 
Now  that  the  earthy  matter  has  been  removed  in  the  slag,  it 
is  far  easier  to  oxidise  the  sulphuret  of  iron  than  it  was  in 
the  first  calcining  process.  To  effect  this,  three  tons  of  the 
granulated  coarse  metal  are  roasted  in  the  calcining  furnace 
(Fig.  32)  for  24  hours,  the  temperature  being  moderated  at 
the  commencement,  to  avoid  fusion,  and  gradually  raised  in 
proportion  as  the  removal  of  the  sulphur  diminishes  the 
fusibility  of  the  charge,  which  is  raked  over  every  two  hours. 
About  one-half  of  the  sulphur  is  converted  by  the  oxygen  of 
the  air  into  sulphurous  and  sulphuric  acids,  which  escape  in 
vapour,  another  portion  of  oxygen  combining  with  the  iron 
from  which  the  sulphur  has  been  removed,  to  form  oxide  of 
iron,  so  that  the  roasted  coarse  metal  consists  essentially  of 
sulphuret  of  copper,  oxide  of  iron,  and  some  unchanged 
sulphuret  of  iron. 

4//$  Process  in  Copper-smelting.  Fusion  of  the  Calcined  Coarse 
Metal  to  remove  all  the  Iron  and  to  obtain  Fine  Metal. — The 
principles  involved  in  this  process  are  the  same  as  in  the 
second  process,  viz.  the  conversion  of  unaltered  sulphuret  of 
iron  into  oxide  of  iron  by  exchange  with  oxide  of  copper 
added  for  that  purpose,  and  the  removal  of  the  oxide  of  iron 
in  the  slag,  in  combination  with  silica. 

The  fusion  is  effected  in  a  furnace  which  does  not  differ 
materially  from  that  employed  in  the  second  process,  except 
that  there  is  no  cavity  in  the  hearth,  which  is  made  to  slope 
from  all  parts  towards  the  tap-hole  (Fig.  34).  The  charge 
consists  of — 

Calcined  coarse  metal  (about  one  ton) 
Roaster-slag  from  the  5th  process  \ 

Refinery-slag  from  the  6th  process 
Ores  containing  oxide  and  carbonate  of  copper] 

(The  roaster  and  refinery  slags  contain  silica  in  combination, 
with  the  oxides  of  iron  and  copper.) 


Melting  for  Fine  Metal  1 1 7 

These  materials  are  fused  together  for  about  six  hours, 
when  they  divide,  as  before,  into  a  regulus  or  matt,  and  a 
'slag  which  remains  above  it.  The  regulus  is  sometimes  run 
out  into  water  (like  the  coarse  metal  of  the  second  process), 
when  it  is  called  fine  metal,  and  sometimes  cast  into  pig- 
moulds  of  sand,  when  it  constitutes  blue-metal,  its  surface 
exhibiting  a  bluish  colour,  due  to  its  still  containing  a  con 
siderable  proportion  of  sulphuret  of  iron,  in  consequence  of 
a  deficiency  of  oxide  of  copper  in  the  charge.  This  regulus 
is  composed  essentially  of  copper  and  sulphur,  and  contains 
about  77  parts  of  copper  in  the  hundred.  The  presence  of 
a  little  sulphuret  of  iron  in  this  regulus  gives  rise  to  consider 
able  differences  in  its  colour  and  appearance,  so  that  it  is 
called  by  several  different  names,  which  do  not  really  imply 
any  important  difference  in  chemical  composition. 

In  some  cases,  when  the  charge  has  contained  an  excess 
of  oxide  of  copper,  the  fine  metal  has  a  red  brown  colour, 
due  to  the  presence  of  much  red  oxide  of  copper  and  metal 
lic  copper,  and  a  pimply  appearance  caused  by  the  escape 
of  sulphurous  acid  gas ;  it  is  then  called  pimple  metal 

When  it  is  intended  to  manufacture  best  selected  copper  for 
making  brass,  gun-metal,  &c.,  the  blue  metal  is  run  into  a 
series  of  sand-moulds.  Since  the  various  impurities  which 
are  present  tend  to  collect  in  a  small  quantity  of  metallic 
copper  which  is  deposited  at  the  bottom  of  the  melted  mass, 
the  pigs  which  are  cast  first  will  be  the  most  impure,  whilst 
the  others  yield  the  best  selected  copper  in  the  subsequent 
operations  of  smelting.  The  first  pigs  yield  bottoms  or  tile- 
copper  (so  called  from  the  shape  of  the  ingots)  when  smelted. 

The  composition  of  a  sample  of  these  bottoms  is  here 
given,  in  100  parts  :  Copper  74,  Tin  14,  Antimony  4!,  Lead 
i,  Iron  2j,  Sulphur  4.  It  is  evident  that  the  metallic 
copper  which  has  separated,  has  decomposed  the  sulphurets 
of  tin,  antimony,  &c.,  contained  in  the  blue  metal,  and  has 
combined  with  those  metals  to  form  an  alloy,  which  is 
heavier  than  the  blue  metal  and  sinks  to  the  bottom. 


1 1 8       Metals :  their  Properties  and  Treatment. 

In  some  smelting-works,  where  the  fine  metal  is  not 
obtained  in  so  pure  a  condition,  and  contains  only  60  parts 
of  copper  in  the  hundred,  it  is  again  submitted  to  the  two 
processes  of  calcining  and  melting,  exactly  as  in  processes 
3  and  4,  when  it  yields  black  copper  or  coarse  copper,  which 
contains  from  70  to  80  parts  of  copper  in  the  hundred. 

The  metal-slag,  as  the  slag  from  the  4th  process  is  termed, 
presents  an  appearance  very  different  from  that  of  the  ore- 
furnace  slag ;  it  is  very  crystalline  and  lustrous,  and  consists 
chiefly  of  oxide  of  iron  combined  with  silica,  but  it  contains 
a  considerable  proportion  of  copper,  partly  in  the  form  of 
an  oxide  in  combination  with  silica,  and  partly  as  small 
particles  of  metallic  copper  disseminated  through  the  mass. 
In  some  specimens  of  the  metal-slag,  the  copper  appears  in 
very  fine  brilliant  filaments  forming  copper-moss.  This  slag 
is  usually  employed  as  part  of  the  charge  in  the  2nd  process 
(melting  for  coarse  metal),  but  it  is  sometimes  fused  in  a 
separate  furnace  with  powdered  coal,  when  a  brittle  matt  is 
obtained  which  contains  a  very  large  proportion  of  copper, 
and  is  called  white  metal,  a  name  which  is  also  occasionally 
applied  to  fine  metal. 

5//£  Process  in  Copper-smelting.  Calcining  or  Roasting 
the  Fine  Metal  to  remove  Sulphur  and  obtain  Blistered  Copper. 
—The  manner  in  which  this  process  is  carried  out  is  varied 
according  to  the  degree  of  purity  of  the  fine  metal,  but  the 
chemical  principles  which  it  involves  are  the  following: 
When  a  compound  of  copper  with  sulphur  is  heated  in  air, 
the  sulphur  combines  with  the  oxygen  of  the  air,  and  is 
thus  gradually  removed  in  the  form  of  sulphurous  acid  gas, 
the  copper  also  combining  with  oxygen,  and  being  left  as 
oxide  of  copper.  Further,  when  an  oxide  of  copper  (or 
compound  of  copper  with  oxygen)  is  melted  in  contact  with 
a  sulphuret  of  copper  (or  compound  of  copper  with  sulphur), 
the  oxygen  of  the  former  combines  with  the  sulphur  of  the 
latter  to  form  sulphurous  acid  gas,  and  the  copper  is  sepa 
rated  in  the  metallic  state. 


Production  of  Blistered  Copper.  1 1 9 

The  pigs  of  blue  metal  are  introduced,  to  the  amount  of 
i-L  ton,  into  a  reverberatory  furnace,  where  they  are  roasted, 
at  a  gradually  increasing  temperature,  so  as  to  avoid  fusion, 
for  about  four  hours,  in  order  that  a  part  of  the  sulphuret 
of  copper  may  be  converted  into  oxide  of  copper.  When  it 
is  judged  that  this  has  been  effected  to  a  proper  extent,  the 
temperature  is  further  raised  so  as  to  fuse  the  materials  upon 
the  hearth,  the  doors  of  the  furnace  being  closed  in  order  to 
avoid  access  of  air.  As  soon  as  the  mass  is  fairly  lique 
fied,  the  temperature  is  somewhat  reduced,  being  again 
raised  towards  the  close.  During  this  fusion,  a  violent 
effervescence  is  observed  in  the  liquid  mass,  due  to  the 
escape  of  sulphurous  acid  gas  formed  by  the  union  of  the 
sulphur  from  the  sulphuret,  with  the  oxygen  from  the  oxide 
of  copper,  whilst  metallic  copper  subsides,  in  a  fused  state, 
and  is  run  out  into  sand-moulds,  where  it  solidifies  into 
ingots  which  preserve  a  blistered  appearance  caused  by  the 
escape  of  sulphurous  acid  during  solidification. 

The  duration  of  the  process  depends  upon  the  degree 
of  purity  of  the  blue  metal  under  treatment,  but  it  varies 
between  12  and  24  hours. 

A  small  quantity  of  slag  (called  roaster-slag)  is  formed 
during  the  fusion,  which  resembles  pumice  in  its  porous 
texture,  but  has  a  dark  red-brown  colour,  and  consists  of  the 
oxides  of  iron  and  copper  combined  with  silica 
derived  partly  from  the  hearth  of  the  furnace, 
and  partly  from  the  sand-moulds  in  which  the 
ingots  of  blue  metal  are  cast.  This  slag  con 
tains  about  1 6  parts  of  copper  in  a  hundred, 
and  is  used  as  a  portion  of  the  charge  in  the 
4th  process. 

The  roasting  furnace  employed  in  this  pro 
cess  is  often  constructed  with  an  air-channel 
(Fig.  37)  traversing  the  whole  length  of  the  fire-bridge,  open 
to  the  air  at  both  ends,  and  communicating  with  the  hearth 
of  the  furnace  through  two  openings  (b  b)  in  the  brickwork. 


1 20      Metals :  their  Properties  and  Treatment. 

This  permits  the  introduction  of  heated  air  into  the  hearth, 
by  which  the  roasting  is  much  facilitated. 

6th  Process  of  Copper-smelting.  Refining  and  Toughening, 
to  purify  the  Copper. — The  pigs  of  blistered  copper  are  far 
from  pure ;  it  contains  considerable  proportions  of  sulphur, 
arsenic,  iron,  tin,  lead  and  other  foreign  substances,  varying 
according  to  the  descriptions  of  ore  employed.  In  order 
to  remove  these  impurities,  the  oxygen  of  atmospheric  air 
is  brought  into  use.  The  furnace  employed  does  not  differ 
very  materially  from  the  melting  furnace  used  in  the  2nd 
process  (Fig.  33),  and  the  blistered  copper  to  be  refined  is 
piled,  in  charges  of  6  or  8  tons,  upon  the  hearth,  in  such  a 
manner  as  to  allow  air  to  circulate  freely  among  the  ingots. 
A  moderate  heat  is  applied  at  first,  to  allow  the  oxygen  of 
the  air  to  act  upon  the  blistered  copper,  an  action  which  is 
facilitated  by  the  porous  structure  of  the  metal.  The  sul 
phur  then  becomes  converted  into  sulphurous  acid  gas, 
and  the  arsenic  into  arsenious  acid  which  passes  off  in 
vapour,  whilst  the  iron,  tin,  lead  and  other  foreign  metals  are 
converted  into  oxides,  as  well  as  a  portion  of  the  copper. 
After  being  roasted  for  about  six  hours,  the  metal  is  melted, 
when  a  thin  layer  of  slag  is  formed  upon  its  surface  ;  after 
raking  this  off,  a  small  sample  of  the  copper  is  withdrawn 
and  examined  by  the  refiner,  who  can  judge  from  the 
appearance  of  its  fracture  how  long  the  subsequent  process 
of  toughening  will  probably  occupy.  In  order  to  toughen 
the  metal,  its  surface  is  covered  with  wood-charcoal  or  an 
thracite,  which  is  renewed  from  time  to  time,  so  as  to  shield 
the  copper  from  further  oxidation,  and  the  melted  metal  is 
stirred  with  a  pole  of  young  wood  (usually  birch)  until  a 
small  sample  half  cut  through  with  a  chisel  and  then  broken, 
exhibits  a  fine  close  grain,  a  silky  fracture,  and  a  light  red 
colour ;  and  a  small  ingot  cast  for  the  purpose  and  ham 
mered  when  red  hot,  is  found  to  be  soft  and  free  from 
cracks  at  the  edges.  The  copper  is  then  said  to  be  at 
tough-pitch)  and  is  taken  out  in  iron  ladles  lined  with  clay, 
and  cast  into  ingots  of  tough-cake  copper. 


Process  of  Poling  Copper.  1 2 1 

The  effect  of  this  process  of  poling,  as  it  is  termed,  in 
toughening  the  copper,  depends  upon  the  removal  of  oxygen 
from  the  metal.  When  the  blistered  copper  has  been  re 
fined,  as  above  described,  by  being  very  slowly  melted  in 
contact  with  air,  it  is  found  to  have  taken  up  a  small  pro 
portion  of  oxygen,  which  is  probably  contained  in  the  metal 
as  an  oxide  (suboxide)  of  copper.  The  presence  of  the  oxy 
gen,  though  it  does  not  amount  to  more  than  two  or  three 
parts  in  a  thousand  of  copper,  has  the  effect  of  rendering 
the  copper  brittle  or  dry,  so  that  a  small  ingot  of  it  cracks 
at  the  edges  when  hammered,  and  its  fracture  exhibits  a  deep 
red  colour  and  a  coarse-grained,  somewhat  crystalline  struc 
ture.  When  the  melted  metal  is  stirred  with  the  pole,  the 
combustible  gases,  generated  from  the  wood  by  the  heat, 
effect  the  removal  of  the  oxygen  from  the  metal,  and  bring 
it  by  degrees  to  tough-pitch.  If,  during  the  operation  of 
casting  the  ingots,  the  surface  of  the  metal  on  the  hearth  be 
not  well  covered  with  charcoal  or  anthracite,  the  copper  will 
go  back  or  become  brittle  again,  in  consequence  of  the  ab 
sorption  of  oxygen  from  the  air. 

If  the  process  of  poling  be  continued  after  the  copper  has 
been  brought  to  tough-pitch,  it  becomes  even  more  brittle 
than  before  it  was  poled,  an  effect  which  was  formerly 
ascribed  to  the  combination  of  the  copper  with  a  little 
carbon  from  the  wood  ;  but  since  analysis  has  failed  to  prove 
the  presence  of  the  carbon,  the  following  less  simple  expla 
nation,  based  upon  experiment,  is  now  generally  received. 
Perfectly  pure  copper  exhibits  the  malleability  and  ductility 
of  the  metal  in  the  highest  perfection,  but  these  qualities  are 
deteriorated  by  the  presence  of  small  proportions  of  the 
various  foreign  matters,  such  as  sulphur,  tin,  antimony,  &c., 
which  cannot  be  entirely  removed  in  the  refining  process. 
The  injurious  effect  of  these  impurities,  however,  is  counter 
acted  in  some  measure  by  the  presence  of  a  small  proportion 
of  oxygen  (not  exceeding  two  parts  in  a  thousand),  so  that  if 
this  element  be  entirely  removed,  the  copper  will  be  over- 
poled,  exhibiting  a  brittle  character  due  to  some  of  the  above- 


122       Metals:  their  Properties  and  Treatment. 

named  impurities.  On  the  other  hand,  if  too  much  oxygen 
has  been  left  in  the  metal,  the  copper  is  dry  or  underpoled. 
The  effect  of  overpoling  upon  the  metal  may  be  remedied 
by  allowing  air  to  act  for  a  short  time  upon  the  melted  cop 
per,  so  that  a  small  quantity  of  oxygen  may  be  absorbed 
by  it. 

When  the  copper  is  intended  for  rolling  into  sheets,  it  is 
usual  to  add  lead,  in  the  proportion  of  about  five  parts  to  a 
thousand  of  copper,  just  before  skimming  the  surface  in  order 
to  ladle  out  the  copper.  The  metal  is  well  stirred  after  the 
addition  of  lead,  in  order  that  the  action  of  the  air  may  pro 
duce  an  oxide  of  lead  which  combines  with  the  oxides  of  tin, 
antimony,  and  other  foreign  metals,  to  form  a  liquid  slag 
which  rises  to  the  surface  of  the  metal  and  is  skimmed  off 
before  casting.  It  is  necessary  that  the  removal  of  the  lead 
from  the  copper  by  oxidation  should  be  as  complete  as  pos 
sible,  since  its  presence  would  prevent  the  scale  of  oxide  of 
copper  from  being  easily  detached  from  the  sheet  during  the 
process  of  rolling,  and  even  -^th  part  of  lead  in  100  parts  of 
copper  suffices  to  injure  its  quality. 

This  treatment  of  the  metal  with  lead  is  called  scarification, 
from  the  scoria  or  slag  which  forms  upon  the  surface. 

The  refinery  slag,  skimmed  from  the  surface  of  the  melted 
copper  before  commencing  the  process  of  poling,  has  a  dull 
brown-red  colour,  with  a  purple  shade,  and  consists  almost 
entirely  of  an  oxide  of  copper  (suboxide)  combined  with 
silica  derived  from  the  hearth  and  from  the  sand-moulds 
employed  to  cast  the  blistered  copper.  It  is  employed  in 
the  4th  process  (fusion  for  fine  metal). 

The  hearths  of  the  copper-furnaces  become  strongly  im 
pregnated  with  copper  in  course  of  time,  and  are  broken  out 
in  order  that  the  metal  may  be  removed  from  them. 

Extraction  of  Copper  from  the  Bituminous  Schists  of  Mans- 
fdd. — Although  most  of  the  copper  sent  into  commerce  is 
extracted  by  the  Welsh  process,  other  methods  are  some 
times  followed  on  the  Continent  for  the  treatment  of  poor 


Extraction  of  Copper  at  Mansfeld. 


123 


ores,  especially  when  'coal  is  not  abundant,  for  the  coal 
required  for  the  Welsh  process  amounts  to  eighteen  times 
the  weight  of  the  copper.  Thus,  at  Mansfeld,  an  ore  is 
extensively  worked,  which  contains  not  more  than  four  parts 
of  copper  in  a  hundred,  in  the  form  of  crystals  of  copper 
pyrites  diffused  through  a  clay  slate  containing  a  large  pro 
portion  of  bituminous  matter.  The  consumption  of  fuel  in 
extracting  the  copper  from  this  ore  is  only  one-third  of  that 
in  the  Welsh  process. 

The  ore  is  first  roasted  in  large  heaps  made  up  with  alter 
nate  layers  of  brush-wood,  the  bituminous 
matter  also  serving  as  fuel.  A  heap  con 
taining  200  tons  of  ore  will  go  on  burning 
for  fifteen  or  twenty  weeks.  In  this  pro 
cess,  which  corresponds  to  the  first  cal 
cination  in  the  Welsh  method,  a  part  of 
the  sulphur  passes  off  as  sulphurous  acid, 
and  much  of  the  iron  is  converted  into 
an  oxide. 

The  next  process  is  similar  to  the 
Welsh  fusion  for  coarse  metal,  and  con 
sists  in  melting  the  roasted  ore  with 
some  fluor  spar,  to  serve  as  a  flux,  some 
copper-ore  containing  carbonate  of  lime, 
for  the  same  purpose,  and  some  slags 
containing  oxide  of  copper  to  decompose 
the  sulphuret  of  iron  and  remove  the 
iron  as  a  silicate  (page  115).  The  fusion 
is  not  conducted  in  a  reverberatory  fur 
nace,  as  in  the  Welsh  process,  but  in  a  small  blast  furnace 
(Figs.  38,  39)  about  14  feet  high,  and  3  feet  in  its  greatest 
width.  The  blast  is  supplied  by  two  tuyeres  (/)  placed 
side  by  side,  about  2  feet  above  the  bottom  of  the  furnace, 
from  which  the  melted  matters  are  conducted  through  two 
channels  (o  o')  into  two  basins  (c  c')  about  3  feet  in  diameter 
and  20  inches  deep,  lined  with  a  mixture  of  clay  and  char 
coal  dust ;  when  one  of  these  basins  is  filled,  the  channel 


FIG. 

emp 

ing    the    Bituminous 

Schists  at  Mansfeld. 


. — Blast-furnace 
iployed  for  smelt 
er  the  1 


124      Metals :  their  Properties  and  Treatment. 


FIG.  39.—  Hearth  of  Blast-furnace 
employed  at  Mansfeld. 


communicating  with  it  is  closed,  and  the  melted  matters 
from  the  furnace  are  run  into  the  other  basin.  The  furnace 
is  provided  with  a  chimney  (G)  30  or  40  feet  high.  The 

fuel  employed  is  either  char 
coal  or  a  mixture  of  char 
coal  and  gas-coke,  which  is 
charged  alternately  with  the 
ore,  as  in  an  iron  blast-fur 
nace.  The  chemical  changes 
which  take  place  in  the  fur 
nace  resemble  those  in  the 
Welsh  process  of  melting  for 
coarse  metal,  and  the  liquid 
matter  which  flows  into  the 
receiving  basins  divides  into  two  portions,  the  lower  layer 
consisting  of  the  sulphurets  of  copper  and  iron,  and  the 
upper  layer  of  slag  composed  chiefly  of  silicate  of  iron 
containing  but  little  copper.  The  slag  is  ladled  out  into 
moulds  and  employed  for  building.  The  matt,  as  the  lower 
layer  is  called,  is  removed  in  crusts,  as  it  solidifies. 

If  the  matt  contains  less  than  thirty  parts  of  copper  in  the 
hundred,  it  is  again  roasted  and  treated  as  before,  so  as  to 
remove  more  of  the  sulphuret  of.  iron  ;  but  if  it  contains 

more  than  this  pro 
portion,  it  is  at  once 
roasted  in  a  special 
open  furnace  (Fig. 
40),  which  consists 
of  six  separate  com 
partments  or  stalls 
with  flues  running  up 
the  back  walls  in 

order  to  create  a  draught.  The  matt  is  placed  upon  a  wood 
fire  in  the  first  compartment,  which  is  then  closed  by  build 
ing  up  a  temporary  wall ;  when  it  has  been  calcined  here  for 
a  certain  time,  it  is  transferred  to  the  second  compartment, 


FIG.  40. — Roasting-stalls  employed  at  Mansfeld. 


Refining  of  Black  Copper  at  Mansfeld.          1 2  5 

and  then  to  the  third.  It  is  now  introduced  into  a  wooden 
vessel  and  washed  with  water  in  order  to  dissolve  the  sul 
phate  of  copper  which  has  been  formed  by  the  combination 
of  the  oxygen  of  the  air  with  the  sulphuret  of  copper.  The 
washed  matt  is  roasted  again  in  the  fourth,  fifth,  and  sixth 
compartments,  in  succession,  being  treated  with  water  after 
every  roasting.  The  solution  of  sulphate  of  copper  thus 
obtained  is  evaporated  and  crystallised,  yielding  blue  vitriol, 
which  is  sent  into  commerce. 

This  operation  of  roasting,  which  lasts  seven  or  eight 
weeks,  corresponds  to  the  calcination  of  the  coarse  metal  in 
the  Welsh  process. 

The  roasted  matt,  containing  oxide  of  iron  and  sulphuret 
of  copper,  is  treated  as  in  the  melting  for  fine  metal,  being 
fused  with  siliceous  slags  which  dissolve  the  oxide  of  iron. 
The  fusion  is  effected  in  a  blast  furnace  similar  to  that  de 
scribed  above,  but  of  smaller  dimensions.  The  liquid  matter 
in  the  receiving  basins  divides  into  three  layers,  the  upper 
most  consisting  of  slag,  the  middle  layer  of  a  matt  containing 
60  or  70  parts  of  copper  in  the  hundred,  combined  with 
sulphur  (representing  the  fine  metal  of  the  Welsh  copper 
smelting),  which  is  again  roasted  and  smelted,  and  the  lowest 
layer  of  black  copper,  which  consists  of  impure  metallic  copper, 
containing  about  95  parts  of  copper  in  the  hundred,  with  3  or 
4  parts  of  iron,  i  part  of  sulphur,  and  sometimes  as  much  as 
120  ounces  of  silver  to  the  ton.  When  a  sufficient  quantity 
of  silver  is  present  to  pay  for  extraction,  the  black  copper 
is  subjected  to  a  process  for  that  purpose,  which  will  be 
described  under  silver,  and  is  afterwards  refined. 

The  refining  of  the  black  copper,  after  separating  the 
silver,  is  conducted  in  a  reverberatory  furnace  (Figs.  41,  42), 
the  hearth  (A)  of  which  is  lined  with  clay  and  powdered 
charcoal,  upon  which  the  black  copper  is  melted  with  the 
flame  of  a  wood  fire  in  the  grate  (F),  and  air  is  thrown  upon 
its  surface  through  two  tuyeres  (/),  when  the  oxygen  of  the 
air  removes  the  sulphur  as  sulphurous  acid,  and  converts  the 


126      Metals:  their  Properties  and  Treatment. 

foreign  metals  into  oxides  which  collect  as  a  slag  upon  the 
surface.     When  the  refining  is  nearly  completed,  a  red  slag 


FIG.  41. — Section  of  Furnace  for  refining  Black  Copper,  at  Mansfeld, 
made  at  the  line  x  of  the  plan,  Fig.  42. 

containing  much  red  oxide  of  copper  forms,  and  a  small 
sample  is  withdrawn  and  carefully  examined  by  forging.  If 
it  be  deemed  sufficiently  pure,  the  copper  is  run  out,  through 


FIG.  42. — Plan  of  Furnace  for  refining  Black  Copper,  at  Mansfeld, 
made  at  the  line  v  u  of  the  section,  Fig.  41. 

the  openings  (a),  into  receiving  basins  (B)  and  removed  in 
rosettes  by  throwing  water  upon  it,  and  taking  off  the  films  of 


Refining  Copper  in  the  German  Hearth.        127 

metal  thus  solidified.  The  rosettes  thus  obtained  consist  of 
dry  copper,  containing  too  large  a  proportion  of  red  oxide. 
It  is  refined  in  the  German  hearth  (Figs.  43,  44)  which  con 
sists  of  a  basin  (c)  about  16  inches  wide,  lined  with  a  mix 
ture  of  clay  and  powdered  charcoal,  and  furnished  with  a 
blast-pipe  (T)  like  that  of  a  blacksmith's  forge.  The  copper 
being  melted  in  this  basin,  is  covered  with  charcoal  and  kept 
fused  until  the  copper  is  at  tough-pitch  in  consequence  of 
the  reduction  of  a  sufficient  proportion  of  the  red  oxide  of 
copper,  the  same  attention  and  judgment  being  necessary 
as  in  the  Welsh  process  of  poling  (page  121).  The  refined 
metal  is  then  ladled  into  ingot-moulds. 


FIG.  43.  FIG.  44. 

German  Hearth  used  for  refining  Rosette  Copper,  at  Mansfeld. 

When  the  black  copper  is  not  rich  enough  to  be  treated 
for  silver,  it  is  at  once  refined  in  the  German  hearth  just 
described,  but  the  process  is  conducted  on  the  principle  of 
the  refining  of  blistered  copper  in  the  Welsh  process,  the 
impurities  being  oxidised  by  the  air  from  the  blast-pipe. 
The  hearth  being  filled  with  glowing  charcoal,  the  black 
copper  is  placed  upon  it  and  gradually  fused  in  the  blast,  so 
that  the  sulphur  may  burn  off  as  sulphurous  acid,  and  the 
foreign  metals  may  be  converted  into  oxides  which  are  run 
off  by  a  channel  provided  for  them.  Alternate  charges  of 
black  copper  and  charcoal  are  added  from  time  to  time,  and 
the  process  continued  until  the  workman  perceives,  by  the 
inspection  of  a  small  sample,  that  the  operation  of  refining 


128      Metals :  their  Properties  and  Treatment. 

is  completed,  when  the  surface  is  skimmed,  and  the  copper 
removed  in  rosettes  which  are  afterwards  toughened  as  de 
scribed  above.  The  rosettes  first  removed  are  sometimes 
rich  in  nickel,  and  are  subjected  to  a  special  treatment  for 
the  extraction  of  that  metal,  which  is  valuable  in  itself  and 
injurious  to  the  quality  of  the  copper. 

VARIOUS    DESCRIPTIONS    OF   COMMERCIAL   COPPER. 

Anglesea  Copper  or  Cement  Copper  is  extracted  from  the 
water  which  is  pumped  out  of  the  Amlwch  mine,  near  Holy- 
head,  and  is  called  blue  water,  its  colour  being  due  to  the  pre 
sence  of  sulphate  of  copper  produced  by  the  action  of  the  air 
upon  the  combination  of  copper  and  sulphur  present  in  the 
ore.  This  water  is  pumped  into  tanks  containing  scrap  iron, 
which  gradually  enters  into  solution  as  sulphate  of  iron,  the 
copper  being  deposited  in  the  metallic  state.  The  fine  red 
colour  of  the  copper,  and  the  pale  green  of  the  sulphate  of 
iron,  give  the  contents  of  the  tanks  a  very  beautiful  appear 
ance,  especially  in  the  sunshine,  and  the  copper  of  cementation 
thus  produced,  being  almost  chemically  pure,  is  of  very  ex 
cellent  quality.  At  Schmollnitz  in  Hungary  cement  copper 
is  also  largely  prepared  in  a  similar  manner. 

Rosette  Copper  or  Rose  Copper  is  made,  chiefly  at  Chessy 
in  France,  by  throwing  water  upon  the  surface  of  the  melted 
copper,  and  removing  the  solidified  metal  in  films  which 
have  a  beautiful  red  coating  of  an  oxide  (suboxide)  of  copper 
formed  by  the  action  of  the  oxygen  of  the  water  upon  the 
metal.  These  rosettes  are  plunged  into  water  as  soon  as 
they  are  removed,  for  if  they  were  allowed  to  cool  in  the  air, 
the  oxygen  would  convert  the  red  oxide  into  a  black  oxide, 
which  would  spoil  the  colour  of  the  copper.  • 

Japan  Copper  resembles  the  preceding,  in  colour,  and  is 
cast  into  ingots  weighing  only  six  ounces  each,  for  exporta 
tion  to  the  East  Indies.  It  is  coloured  by  being  thrown  into 
water  as  soon  as  the  ingot  has  solidified. 

Copper  is  sometimes  cast  into  thin  plates  by  pouring  into 


Effect  of  Impurities  on  Copper.  1 29 

the  mould  enough  metal  to  form  a  single  plate,  which  is 
allowed  to  cool  before  pouring  in  a  fresh  quantity,  when  a 
film  of  suboxide  of  copper  is  formed  upon  the  surface  of  the 
first  plate,  which  prevents  it  from  adhering  to  the  next,  so 
that  the  plates  are  easily  separated  when  the  moulding-case 
is  removed. 

Sean-shot  Copper  is  made  by  pouring  melted  copper  through 
a  perforated  ladle  into  a  vessel  of  hot  water,  when  it  forms 
round  fragments  like  shot,  which  are  very  convenient  for  the 
manufacture  of  brass.  When  cold  water  is  used,  the  metal 
is  obtained  in  flakes,  which  are  termed  feathered  shot.  In 
order  to  remove  the  scale  of  oxide  from  rolled  copper  sheet 
ing,  before  sending  it  into  the  market,  the  somewhat  in 
explicable  course  is  adopted  of  soaking  them  for  a  few  days 
m  urine,  then  heating  them  in  a  reverberatory  furnace, 
rubbing  them  with  a  piece  of  wood,  and  plunging  them 
when  hot  into  water,  when  the  scale  detaches  itself.  The 
sheets  are  then  smoothed  between  rollers. 

Effect  of  the  presence  of  Foreign  Matters  upon  the  quality  of 
Copper.— From  the  circumstance  that  the  refiner  tests  the 
quality  of  copper  by  forging  a  hot  sample,  it  will  be  inferred 
that  the  effect  of  impurities  upon  its  malleability  and  tenacity 
is  more  perceptible  at  a  high  than  at  a  low  temperature. 
The  foreign  matters  which  commercial  copper  is  liable  to 
contain  are  arsenic,  sulphur,  antimony,  tin,  bismuth,  lead, 
silver,  iron,  and  nickel.  Of  these,  sulphur  and  antimony  are 
generally  considered  the  most  injurious  in  diminishing  the 
malleability  and  tenacity  of  the  metal.  Arsenic  is  very  com- 
monly  found  in  copper,  amounting,  in  come  of  the  Spanish 
coppers,  to  as  much  as  one  part  in  a  thousand,  and  was 
formerly  supposed  to  be  as  injurious  to  the  quality  of  the 
copper  as  antimony  is,  but  modern  experience  has  shown 
that  copper  may  be  easily  rolled  and  drawn  into  wire  even 
when  it  contains  a  considerable  proportion  of  arsenic.  A 
small  proportion  of  tin  is  believed  to  increase  the  toughness 
of  copper,  but  bismuth  and  nickel  have  the  opposite  effect. 

K 


130      Metals:  their  Properties  and  Treatment. 

The  conducting  power  of  copper  for  electricity  is  reduced 
in  a  most  striking  manner  by  the  presence  of  foreign  matters, 
so  that,  in  the  construction  of  telegraphic  apparatus,  it  is 
important  that  the  purest  attainable  copper  wire  should  be 
employed.  Pure  copper  is  scarcely  inferior  to  silver  (see 
p.  9)  in  its  conducting  power,  and  the  conducting  power  of 
the  native  copper  from  Lake  Superior,  which  is  almost  pure, 
stands  to  that  of  pure  copper  in  the  proportion  of  93  to  100, 
whilst  the  Australian  (Burra  Burra)  copper,  also  very  pure, 
has  a  conducting  power  of  89,  and  the  Spanish  copper, 
which  contains  much  arsenic,  has  a  conducting  power  only 
one-seventh  of  that  of  pure  copper,  or  in  the  proportion  of 
14  to  100. 

The  addition  of  a  small  proportion  of  phosphorus  (about 
five  parts  in  a  thousand)  to  copper  is  found  to  harden  it  and 
somewhat  to  increase  its  tenacity  ;  it  is  also  said  to  render  it 
less  liable  to  corrosion  when  exposed  to  the  action  of  sea- 
water. 

By  adding  arsenic  to  copper,  in  about  the  proportion  of 
one  to  ten,  a  white  somewhat  malleable  metal  is  obtained, 
which  is  not  easily  tarnished  by  air,  and  is  much  hardei 
than  copper.  This  compound,  which  is  employed  for  clock 
dials  and  for  thermometer  and  barometer  scales,  is  made  by 
heating  five  parts  of  copper  clippings  with  two  parts  of  white 
arsenic  (arsenious  acid)  arranged  in  alternate  layers  and 
covered  with  common  salt,  in  a  covered  earthen  crucible. 


TIN. 

This  metal  is  scarcely  (if  ever)  found  in  the  metallic  state, 
but  is  extracted  from  the  ore  known  as  tinstone,  which  is  an 
oxide  of  tin,  or  combination  of  the  metal  with  oxygen. 
Cornwall  has  been  noted  for  its  tin  mines  from  a  very  remote 
period  \  tinstone  is  also  found  in  Bohemia,  Saxony,  Malacca 


Treatment  of  Tin  Ores.  131 

and  Banca,  the  straits  tin  obtained  from  the  last-named 
localities  being  much  valued  on  account  of  its  purity.' 
Siberia,  Sweden,  North  and  South  America,  and  Australia 
also  furnish  tin  ore,  though  in  smaller  quantity.  Tinstone  is 
found  either  as  stream  tin  ore  or  mine  tin  ore.  The  former  is 
also  called  alluvial*  tin  ore  from  its  occurrence  in  the  mine 
ral  matter  deposited  by  torrents  in  the  valteys  adjacent  to 
the  veins  of  mine  tin  ore,  and  is  much  purer  than  the  latter, 
because  it  has  been  mechanically  separated,  by  the  action  of 
the  stream,  from  the  foreign  minerals  which  were  associated 
with  it  in  the  vein.  Occasionally,  it  is  found  in  well-formed 
prismatic  crystals  which  are  perfectly  pure  oxide  of  tin.  The 
mine  tin  ore  occurs  in  veins  traversing  rocks  of  quartz, 
granite,  or  clay-slate,  where  it  is  associated  with  arsenical 
pyrites  (see  p.  104),  copper  pyrites,  specular  iron  ore,  and  a 
remarkably  heavy  crystalline  mineral  called  wolfram  (tungs- 
tate  of  iron  and  manganese)  which  consists  of  tungstic  acid 
(an  oxide  of  the  metal  tungsteti)  combined  with  the  oxides 
of  iron  and  manganese.  In  order  to  obtain  the  tinstone  in 
a  sufficiently  pure  state  for  smelting,  the  ore  is  stamped  to 
powder,  washed,  and  calcined. 

The  processes  which  are  put  in  operation  in  order  to 
obtain  marketable  tin  from  the  raw  ore  may  be  summed  up 
under  the  following  heads  : 

1.  Mechanical  preparation  of  the  ore. 

2.  Calcining  or  roasting. 

3.  Washing  the  roasted  ore. 

4.  Smelting. 

5.  Refining. 

i.  Mechanical  Preparation  of  Tin  Ores.— The  mine  tin  ore, 
as  it  is  raised  from  the  mine,  is  roughly  cleansed  from  earthy 
matters  by  washing  it  upon  a  grating  under  a  stream  of 
water.  It  is  then  picked  over  and  broken  with  a  mallet,  the 
pieces  of  copper  pyrites  being  placed  aside  to  be  smelted  for 

*  Alhwio  (Latin),  an  inundation. 
K  2 


132      Metals:  their  Properties  and  Treatment. 

that  metal,  and  the  iron  and  arsenical  pyrites  rejected. 
The  tin  ore  is  then  crushed  in  the  stamp-chest  (c,  Fig.  45) 
which  is  a  wooden  trough  lined  at  the  bottom  with  stamped 
ore,  and  provided  with  a  number  of  massive  wooden 
stampers  (B)  shod  with  blocks  of  cast  iron  weighing  about 
i\  cwts.  These  are  raised  by  cams  fixed  to  an  axle  (A) 
which  is  made  to  revolve  by  water  or  steam  power,  so  that 
each  stamper  may  give  about  twenty  blows  in  a  minute,  fall 
ing  through  a  space  of  8  or  10  inches.  These  heavy  blows 


FIG.  45. — Section  of  Stamping-mill. 

speedily  reduce  the  ore  to  powder,  and  a  stream  of  water, 
which  constantly  flows  into  the  trough,  carries  this  powder 
through  openings  in  one  side  of  it  which  are  closed  with  iron 
plates  perforated  with  about  160  holes  in  the  square  inch,  so 
that  the  larger  fragments  may  not  pass  through.  The  holes 
in  the  iron  plates  are  conical,  having  their  narrower  open 
ings  inside  the  trough,  to  prevent  them  from  becoming 
choked.  The  water  carries  the  powdered  ore  into  a  series 
of  reservoirs,  in  which  the  ore  settles  down,  whilst  the  water 


Treatment  of  Tin  Ores.  \  3  3 

flows  away.     Since  the  tinstone  is  much  heavier  than  the 
other  substances  present  in  the  ore  (its  specific  gravity  being 


FIG.  46. — Rack  for  washing  Ores. 

6 -5)  the  greater  part  of  it  is  deposited  in  the  first  reservoir, 
the  successive  deposits  becoming  poorer  as  the  stream  flows 
on,  and  the  sand,  which  has  a  specific  gravity  of  about  27, 


FIG.  47. — Section  of  Rack  for  washing  Ores 


being  in  great  measure  carried  away.  Various  mechanical 
contrivances  are  adopted  for  effecting  a  further  purification 
of  the  slimes  deposited  in  the  reservoirs,  in  all  of  which 


j  34      Metals :  their  Properties  and  Treatment. 

advantage  is  taken  of  the  high  specific  gravity  of  the  tinstone. 
The  rack  (Figs.  46,  47)  which  may  serve  as  an  illustration  of 
these,  is  an  inclined  plane  of  wood  with  a  shallow  ledge  (g), 
about  9  feet  long,  having  one  end  5  or  6  inches  higher  than 
the  other.  It  is  swung  upon  a  pivot  (p)  at  each  end,  so 
that  it  may  be  tipped  and  its  contents  emptied  over  the  side. 
About  25  Ibs.  of  the  slimes  are  spread  upon  an  inclined 
shelf  (H),  whence  they  are  washed  by  a  stream  of  water  on 
to  the  inclined  plane  (F),  when  the  sand  and  other  earthy 
portions  are  carried  away  by  the  water,  whilst  the  heavier 
tinstone,  with  some  pyrites,  &c.,  are  left  upon  the  plane; 
the  deposit  formed  upon  the  higher  portion  of  the  incline  is 
fit  for  the  second  process  (calcining  or  roasting),  but  that 
formed  on  the  lower  part  requires  another  washing.  When 
a  sufficient  quantity  of  deposit  has  been  collected  on  the 
table,  the  latter  is  tipped  up  sideways,  and  the  upper  and 
lower  deposits  allowed  to  fall  into  separate  receptacles. 

The  buddle  is  a  fixed  inclined  plane  worked  in  a  similar 
manner.  The  tossing-tub,  dolly  or  kieve,  is  a  tub  in  which 
powdered  ore  is  stirred  up  with  water  and  allowed  to  settle, 
the  subsidence  being  hastened  by  striking  the  sides  of  the 
tub  ;  the  lower  part  of  the  sediment  is  of  course  the  richest 
in  the  heavier  tin  ore. 

2.  Calcining  or  Roasting  the  Tin  Ore. — The  arsenical  pyrites 
and  copper  pyrites  are  too  heavy  to  be  entirely  removed  by 
stamping  and  washing,  so  that  the  ore  is  next  treated  in  the 
burning-house,  where  it  is  roasted  in  order  to  expel  the 
arsenic  and  sulphur.  This  is  effected  in  reverberatory  fur 
naces,  furnished  with  horizontal  flues  several  hundred  yards 
long,  in  which  the  white  arsenic,  formed  by  the  arsenic  in 
the  pyrites  and  the  oxygen  of  the  air,  is  deposited  in  the 
solid  state.  From  6  to  8  cwts.  of  prepared  ore  is  roasted  at 
once,  the  temperature  being  very  moderate  at  first,  to  avoid 
the  fusion  of  the  pyrites,  and  the  ore  being  frequently  raked 
over  to  expose  fresh  surfaces  to  the  oxidising  action  of  the 
air.  The  roasting  occupies  from  12  to  18  hours,  and  when 


Roasting  of  Tin  Ore. 


135 


FIG.  48.— Brunton's  Calciner. 


136      Metals :  their  Properties  and  Treatment. 

it  is  completed,  nearly  the  whole  of  the  arsenic  has  been 
expelled  in  the  form  of  vapour  of  arsenious  acid  (white 
arsenic),  and  much  of  the  sulphur  in  the  pyrites  has  com 
bined  with  oxygen,  and  passed  off  as  sulphurous  acid  gas  ; 
a  great  portion  of  the  sulphuret  of  copper  in  the  copper  py 
rites  has  also  combined  with  oxygen  to  form  sulphate  of 
copper,  a  change  which  is  completed  by  allowing  the  roasted 
ore  to  remain  exposed  to  the  air,  in  a  moist  state,  for  some  days. 
Bruntorfs  Caldner  (Fig.  48),  which  is  adopted  in  some 


FIG.  49.—  Saxon  Furnaces  for  calcining  Tin  Ore.  a,  Hearth.  Z>,  Grate. 
d,  Fire-bridge,  g,  Chimney,  h.  Flue,  i,  Channel  for  conveying  the 
fumes  into  the  condensing  chambers. 

works  for  roasting  tin  ores,  consists  of  a  circular  table  (T)  of 
cast  iron  8  or  10  feet  in  diameter,  covered  with  fire-brick, 
made  to  revolve  at  three  or  four  turns  in  an  hour  on  the  hearth 
of  a  reverberatory  furnace  with  two  grates.  The  tin  ore  is 
allowed  to  fall  from  a  hopper  (H)  upon  the  centre  of  the  table, 
where  it  is  distributed  and  turned  over  by  the  spider  (s),  an 
iron  frame  with  projecting  arms,  which  is  suspended  from  the 
arch  of  the  furnace.  By  one  of  these  arms  the  ore  which 
has  been  gradually  carried,  by  the  rotatory  motion,  to  the 
circumference,  is  delivered,  in  a  roasted  condition,  through 


Smelting  of  Tin  Ore.  137 

an  aperture  (o)  under  the  chimney.  In  this  furnace  the 
roasting  operation  is  carried  on  without  interruption. 

In  Saxony,  the  roasting  is  conducted  by  a  wood  fire  in 
reverberatory  furnaces  (Fig.  49)  connected  with  a  flue  above 
100  feet  long,  in  which  the  arsenious  acid  (white  arsenic) 
produced  by  the  oxidation  of  the  arsenical  pyrites  is  de 
posited.  12  cwts.  are  roasted  in  each  furnace  in  24  hours, 
yielding  5  or  6  cwts.  of  white  arsenic. 

Common  salt  is  sometimes  added  to  the  tin  ore  pre 
viously  to  the  roasting,  when  the  chloride  of  sodium  con 
verts  part  of  the  arsenic  and  sulphur  into  chlorides  which 
pass  off  in  the  form  of  vapour. 

3.  Washing  the  Roasted  Tin  Ore. — The  next  process  con 
sists  in  stirring  the   roasted  ore  with  water,  in  a  wooden 
tank,  when  the  sulphate  of  copper  is  dissolved  by  the  water, 
and  is  drawn  off  after  the  ore  has  settled  down,  the  copper 
being  recovered  from  the  solution  by  leaving  it  in  contact 
with  iron,  as  in  the  case  of  the  blue  water  of  the  Anglesea 
copper-mines  (p.  128).     By  another  washing  upon  the  rack, 
or  some  similar  arrangement,  the  lighter  oxide  of  iron  pro 
duced  by  the  roasting  of  the  pyrites  is  now  removed,  and 
the  prepared  tin  ore  or  black  tin,  containing  above  60  parts 
of  tin  in  the  hundred,  is  ready  for  smelting. 

4.  Smelting  the  prepared  Tin  Ore. — The  furnaces  (Fig.  50) 
generally  employed  in  the  smelting-houses  of  Cornwall  are 
reverberatory  furnaces,  having  a  low  arch,  with  air  channels 
under  the  fire-bridge  and  hearth,  to  prevent  injury  from  the 
high  temperature,  the  draught  being  produced  by  a  chimney 
40  or  50  feet  high.     Coal  is  burnt  upon  the  grate,  the  flame 
of  which  heats  the  material  upon  the  hearth.     About  a  ton 
of  the  prepared  ore  (oxide  of  tin)  is  mixed  with  one-fifth  to 
one-eighth  of  its  weight  of  ground  anthracite  coal,  and  with 
a  little  lime  which  is  intended  to  flux  or  liquefy  the  small 
quantity  of  silica  still  mingled  with  the  ore.     Occasionally 
fluor  spar  is  added  with  the  same  object.     The  mixture  is 
damped  with  water,  to  prevent  it  from  dusting,  and  thrown 


138       Metals :  their  Properties  and  Treatment. 


upon  the  hearth  of  the  reverberatory  furnace.  The  doors 
are  closed,  but  the  temperature  is  kept  low  at  first,  for  other 
wise  the  oxide  of  tin  would  combine  with  the  silica  and  the 
lime  to  form  a  glass  or  slag,  causing  a  great  loss  of  tin.  By 
exposing  the  charge  to  a  gradually  increasing  temperature 
during  about  six  hours,  the  oxide  of  tin  is  made  to  part  with 
its  oxygen  to  the  carbon  of  the  coal,  yielding  metallic  tin, 
which  melts  and  is  partly  collected  in  the  hollow  of  the 
hearth.  But  as  tin  is  a  very  light  metal  (specific  gravity  7 '3), 
and  the  slag  inclines  to  be  pasty,  it  is  necessary  for  the 


FIG.  50. — Furnace  for  smelting  Tin  Ores.  A,  Fire-door.  B,  Charging-door. 
C,  Working-door.  E,  Door  for  moderating  the  draught  whilst  charging 
the  furnace,  lest  the  ore-dust  be  blown  into  the  flue.  F,  Air-channel 
under  hearth. 

smelter  to  stir  the  melted  mass  in  order  to  facilitate  the 
separation  of  the  tin.  The  temperature  is  raised  very  con 
siderably  towards  the  end  of  the  operation,  in  order  to  render 
the  slag  as  liquid  as  possible,  so  that  it  may  not  retain  too 
much  tin  entangled  in  it.  The  slag  is  then  raked  out  of  the 
furnace,  and  the  melted  tin  is  run  out  into  a  cast-iron  pan, 
where  it  is  allowed  to  remain  for  some  time,  in  order  that 
any  slag  may  rise  to  the  surface,  after  which  it  is  skimmed 
and  poured  into  cast-iron  ingot  moulds. 

The  slag  raked  out  of  the  furnace,  which  is  essentially  a 


L  iquation  and  Boiling.  1 39 

combination  of  silica  with  oxide  of  iron,  alumina,  oxide  of 
tin,  and  lime,  containing  as  much  as  T!¥th  of  its  weight  of 
tin  in  the  form  of  oxide  (beside  the  metal  disseminated 
through  it),  is  sorted  into  three  kinds.  About  three-fourths 
of  it,  containing  very  little  metallic  tin,  is  thrown  away ; 
another  portion,  with  which  small  globules  of  tin  are  inter 
mixed  to  the  amount  of  about  five  parts  in  the  hundred,  is 
subjected  to  the  stamping  process  (p.  132),  whilst  a  third 
portion,  taken  from  the  surface  of  the  melted  tin,  is  so  rich 
in  globules  of  metal  that  it  is  worked  again  in  the  furnace. 
About  if  ton  of  coal  is  consumed  as  fuel  for  each  ton  of 
metallic  tin  smelted  by  this  furnace. 

5.  Refining  the  Metallic  Tin. — The  ingots  of  tin,  as  obtained 
from  the  smelting-furnace,  contain  various  impurities.  Not 
only  are  particles  of  slag,  and  of  the  oxide  of  tin,  entangled 
in  the  metal,  but  small  quantities  of  iron,  arsenic,  copper, 
sulphur,  and  tungsten  are  present  in  it,  and  must  be  re 
moved  in  order  to  obtain  marketable  tin.  This  is  effected 
by  successive  operations  which  are  known  as  liquation  and 
boiling. 

The  process  of  liquation  consists  in  melting  out  the  tin 
and  leaving  the  impurities  behind.  The  ingots  of  tin  are 
moderately  heated  upon  the  hearth  of  a  reverberatory  furnace 
similar  to  that  employed  for  smelting  the  ore,  when  the  bulk 
of  the  metal  liquefies  and  is  allowed  to  flow  out  of  the  furnace 
into  a  refining-basin,  leaving  a  residue  of  impurities  upon  the 
hearth.  Fresh  ingots  are  introduced  from  time  to  time,  until 
about  five  tons  of  tin  have  collected  in  the  refining-basin, 
which  is  the  case  in  about  an  hour  after  the  commencement 
of  the  process. 

The  boiling  consists  in  plunging  into  the  tin  contained  in 
the  refining-basin,  which  is  heated  by  a  separate  fire,  stakes 
or  logs  of  wet  wood  which  are  held  down  under  the  metal 
by  a  kind  of  clamp  fixed  above  the  refining-basin. 

The  heat  of  the  melted  metal  causes  a  brisk  evolution  of 
steam,  which  produces  all  the  appearance  of  boiling  in  the 


140       Metals :  their  Properties  and  Treatment. 

tin,  and  carries  the  entangled  impurities  up  to  the  surface  in 
a  froth  which  is  skimmed  off.  After  about  three  hours,  the 
wood  is  taken  out,  and  the  melted  tin  allowed  to  remain 
quiet  for  two  hours,  when  the  foreign  matters  which  still 
remain  dissolved  in  the  tin  gradually  accumulate  towards  the 
bottom  of  the  basin,  leaving  the  upper  part  of  the  metal 
nearly  pure.  (Sometimes  tossing  is  substituted  for  boiling, 
that  is,  the  tin  is  well  agitated  by  raising  a  ladleful  of  the 
metal  to  a  considerable  height,  and  pouring  it  into  the  bath.) 
The  tin  is  then  ladled  out  into  moulds,  either  of  granite  or 
cast  iron,  and  cast  into  ingots  weighing  about  3  cwt.  each,* 
those  cast  from  the  upper  or  purer  part  of  the  metal  being 
distinguished  as  refined  tin,  those  from  the  middle  layer  as 
block  tin,\  and  those  from  the  bottom  being  so  impure  that 
they  must  be  again  subjected  to  the  refining  process.  The 
refined  tin  is  very  brittle  at  a  temperature  somewhat  below 
its  melting  point,  so  that  when  the  ingots  are  heated  and 
allowed  to  fall  from  a  height,  they  break  up  into  irregular 
prismatic  fragments  which  are  called  grain  tin.  The  refiner 
tests  the  purity  of  the  tin  by  casting  a  small  quantity  in  a 
stone  ingot  mould,  when  the  refined  tin  remains  bright  and 
smooth,  after  cooling;  the  block  tin  becomes  frosted  or 
crystalline,  and  the  impure  tin  has  a  yellowish  colour. 

The  metallic  residue  left  upon  the  hearth  in  the  process 
of  liquation  allows  tin  of  inferior  purity  to  melt  out  when  a 
stronger  heat  is  applied ;  this  is  run  out  into  a  small  iron 
basin,  allowed  to  rest,  and  the  upper  part  of  the  melted  metal 
ladled  into  moulds  to  be  afterwards  refined :  a  white  brittle 
alloy  containing  tin,  iron,  and  other  foreign  metals  is  found 
deposited  at  the  bottom  of  the  basin. 

The  refined  tin  will  contain  99^  parts  of  tin  in  the  hundred, 
the  common  or  block  tin  98^  parts,  and  the  last  portion, 

*  Banca  tin  is  sold  in  blocks  of  40  and  120  Ibs.  each  ;  Malacca  tin  in 
pyramids  weighing  about  I  Ib.  each. 

f  This  must  not  be  confounded  with  block-tin  plate  of  which  kettles, 
saucepans,  &c.,  are  made,  which  is  not  tin,  but  iron  plate  covered  with 
a  layer  of  tin. 


Smelting  of  Tin  Ore  in  the  Blast-furnace.      141 

which  requires  a  second  refining,  contains  only  95  parts. 
The  temperature  at  which  tin  is  melted  before  casting  is  said 
to  be  of  importance,  its  malleability  being  injured  if  it  be 
cast  at  too  low  a  temperature. 

Reduction  of  Stream  Tin  Ore  in  the  Blast-furnace  or  Blow 
ing-house. This  operation  is  attended  with  greater  consump 
tion  of  fuel  and  loss  of  tin  than  that  practised  in  England, 
but  it  is  largely  employed  in  the  tin-works  of  Saxony.  The 
blast-furnace  (A,  Fig.  51)  is  only  ten  feet  high,  cylindrical  in 
shape,  and  surmounted  by  a  conical  hood  divided  into  com 
partments  for  collecting  the 
dust  carried  up  by  the 
blast,  which  is  forced  in  by 
a  blast-pipe  at  o,  near  the 
bottom  of  the  furnace.  The 
sides  and  bottom  of  the 
furnace  are  built  of  granite, 
the  bottom  (D)  being  a 
single  block  hollowed  out 


I 


m 


i  •  v 


' 


FIG.  51. — Blast-furnace  or  Blowing-house 
for  smelting  Tin  Ores. 


for  the  reception  of  the  tin 
which  flows  out,  together 
with  the  slag,  into  a  basin 
of  granite  (B)  lined  with  a 
coating  of  clay  and  char 
coal.  If  the  tin  ore  con 
tains  much  oxide  of  iron, 

some  quartz  is  employed  as  a  flux ;  but  if  much  silica  is 
already  contained  in  the  ore,  lime  or  finery  cinder  (p.  52)  is 
employed  to  form  a  fusible  slag. 

The  prepared  tin  ore  and  wood  charcoal  are  constantly 
charged  in  at  the  top  of  the  furnace,  so  as  to  keep  it  full, 
when  the  carbonic  oxide,  produced  by  the  combination  of 
the  carbon  with  the  oxygen  of  the  air,  abstracts  the  oxygen 
from  the  oxide  of  tin  (see  p.  31),  and  the  metallic  tin  runs 
down  to  the  bottom  of  the  furnace,  accompanied  by  a  small 
quantity  of  slag  formed  by  the  fusion  of  the  silica  in  the  ore 


142      Metals :  their  Properties  and  Treatment. 


with  the  ashes  of  the  charcoal,  and  runs  out  into  the  fore- 
hearth  (B),  from  which  the  slag  is  removed  into  a  tank  of 
water,  the  tin  remaining  liquid  in  the  basin.  When  the 
latter  is  full  of  tin,  it  is  discharged,  through  a  tap-hole,  into 
an  iron  basin  (c),  where  it  is  further  treated  like  the  tin  ob 
tained  by  liquation  (p.  139).  The  loss  of  tin  in  the  blowing- 
houses  is  twice  or  three  times  as  great  as  in  the  smelting- 
houses. 

At  Altenberg,  in  Saxony,  where  the  ores  contain  bismuth, 
they  are  treated,  after  roasting,  with  muriatic  acid,  for  the 

extraction  of  that  metal. 
The  Saxony  tin  generally 
contains  a  little  bismuth. 

Treatment  of  Tin*  Ores 
containing  Wolfram. — Since 
wolfram  is  even  heavier  than 
tinstone,  its  specific  gravity 
being  7-5,  and  that  of  tin 
stone  6 -5,  the  tin  ore  can 
not  be  freed  from  wolfram 
by  washing.  Moreover,  the 
compounds  of  tungstic  acid 
obtained  from  wolfram  have 
received,  of  late  years,  some 
important  applications  in 
the  useful  arts ;  thus  tung- 

state  of  soda  is  employed  as  a  mordant  by  the  calico-printer, 
and  is  the  most  effective  application  for  rendering  muslin 
uninflammable;  tungstate  of  baryta  is  employed  as  a  sub 
stitute  for  white  lead.  Accordingly,  when  the  prepared  tin  ore 
contains  any  considerable  proportion  of  wolfram,  the  quan 
tity  of  this  latter  is  ascertained  by  chemical  analysis,  and 
enough  sulphate  of  soda  (salt-cake  from  the  alkali-works)  is 
added  to  furnish  a  little  more  soda  than  is  necessary  to 
form  tungstate  of  soda  with  the  tungstic  acid  which  is  pre 
sent.  Some  coal  dust  is  added  to  the  mixture,  which  is  then 


FIG.  52. — Blowing-house  at  Altenberg. 
F,  Crucible.  G,  Inclined  plane  for 
slag.  I,  Fore-hearth. 


Treatment  of  Tin  Ore  containing  Tungsten.     143 

heated  on  the  cast-iron  hearth  of  a  reverberatory  furnace, 
when  the  carbon  removes  the  oxygen  from  the  sulphate  of 
soda,  leaving  a  combination  of  sulphur  with  sodium  (sul- 
phuret  of  sodium).  A  little  air  is  then  allowed  access  to  the 


FIG.  53. — Reverberatory  Furnace  for  manufacture  of  Tungstate  of  Soda  from 
Tin  Ores.  B,  Opening  for  introducing  the  charge.  D,  Working-door. 
Happening  for  discharging  the  contents  of  the  hearth.  F,  Vault  for  re 
ceiving  the  finished  charge. 

heated  mass,  when  its  oxygen  converts  the  sulphur  into  sul 
phurous  acid  gas,  and  the  sodium  into  soda,  which  combines 
with  the  tungstic  acid  to  form  tungstate  of  soda.  The 
furnace  (Fig.  53)  is  so  constructed  that  the  flame  from  the 


144      Metals :  their  Properties  and  Treatment. 

grate  (c),  after  passing  over  the  hearth  (A)  of  the  furnace, 
may  return  underneath  it,  so  as  to  heat  the  charge  uniformly. 
The  mass  is  transferred  from  the  furnace  into  tanks  of  water 
which  dissolves  the  tungstate  of  soda,  to  be  afterwards  ob 
tained  in  crystals  by  evaporating  the  solution.  The  oxides 
of  iron  and  manganese  derived  from  the  wolfram  are  still 
contained  in  the  tin  ore,  but  they  are  so  much  lighter  that 
they  can  easily  be  separated  from  it  by  washing,  when  the 
tin  ore  is  ready  to  be  smelted  in  the  usual  way. 

Tin  is  remarkable  for  its  property  of  creaking  when  bent ; 
a  bar  of  the  metal,  when  bent  to  and  fro,  emitting  a  sound 
as  if  grains  of  sand  were  intermixed  with  the  particles  of 
metal.  It  has  been  noticed,  in  the  general  consideration  of 
the  properties  of  metals  (p.  10),  that  tin  is  more  easily 
melted  than  any  other  simple  metal  in  common  use,  and 
that  it  is  possessed  of  a  high  degree  of  malleability,  which  is 
turned  to  advantage  in  the  manufacture  of  tin-foil,  by  rolling 
and  hammering  the  metal  into  extremely  thin  leaves. 

Tin  is  so  little  acted  upon  or  corroded  by  air  or  by  weak 
acids,  that  it  is  employed  as  a  coating  to  protect  the  surfaces 
of  other  metals,  such  as  iron,  copper,  and  brass.  Tin-plate 
is  iron  covered  with  a  thin  coating  of  tin,  and  since  its 
manufacture  is  an  important  branch  of  English  industry,  an 
outline  of  it  may  be  here  given. 

Manufacture  of  Tin-plate. — The  sheet  iron  employed  for 
the  manufacture  of  the  best  tin-plate  is  refined  with  charcoal 
(p.  51),  though  iron  refined  with  coke  is  sometimes  em 
ployed,  the  tin-plate  being  distinguished  accordingly  as  char 
coal-plate  and  coke-plate.  The  last  term,  however,  now  usually 
refers  to  plate  which  has  been  made  from  puddled  iron.  A 
somewhat  red-short  (p.  69)  iron  from  the  Forest  of  Dean 
is  extensively  employed  for  the  purpose,  being  possessed  of 
great  toughness  when  cold. 

In  order  to  obtain  iron  plates  of  the  required  thickness, 
the  bars,  |ths  of  an  inch  thick,  are  cut  into  pieces  15  inches 
long  and  6  inches  wide.  Each  of  these,  having  been  heated 


Manufacture  of  Tin  Plate.  145 

to  redness,  is  rolled  until  its  width  is  increased  to  15  inches. 
It  is  then  again  heated,  and  rolled  in  the  opposite  direction 
until  it  is  5^-  feet  long.  The  plate  is  next  sprinkled  with  a 
little  coal-dust  to  prevent  it  from  sticking  together,  doubled, 
again  heated,  and  passed  between  very  smooth  rollers  until 
the  original  length  of  the  doubled  plate  (2f  feet)  has  been 
increased  to  five  feet.  After  being  again  doubled  and 
heated,  the  four-fold  plate  is  rolled  out  from  30  inches  to  43 
inches.  It  is  then  cut  to  the  proper  dimensions  (not  exceed 
ing  1 8  inches  by  13),  the  plates  separated,  and  prepared  for 
tinning.  At  this  stage  they  are  termed  black  plates. 

The  plates  must  be  rendered  perfectly  clean  and  bright, 
for  the  slightest  impurity  would  prevent  the  proper  adhesion 
of  the  tin. 

(1)  The  plates  are  bent  so  that  they  will  stand  on  end, 
and  arranged  in  a  reverberatory  furnace  in  order  that  they 
may  be  heated  to  redness. 

(2)  They  are  immersed  in  a  mixture  of  four  pounds  of 
muriatic  acid  with  three  gallons  of  water  for  a  few  minutes, 
after  which  they  are 

(3)  Again  heated  to  redness,  when  the  oxide  of  iron  comes 
off  the  surface  in  scales. 

(4)  They  are   hammered  straight    and   passed   between 
rollers  of  cast  iron  hardened  by  chilling  (p.  57). 

(5)  The  plates  are  placed  separately,  on  their  edges,  in  sour 
bran- water,  and  occasionally  turned,  for  ten  or  twelve  hours. 

(6)  They  are  pickled,  that  is,  immersed  and  stirred  about 
for  an  hour,  in  a  leaden  trough  containing  diluted  sulphuric 
acid,  at  a  temperature  of  90°  or  100°  F.,  until  they  are  per 
fectly  bright,  the  acid  having  dissolved  off  all  the  oxide.    The 
sulphuric  acid  employed  must  be  free  from  arsenic,  which  is 
apt  to  produce  black  spots  upon  the  metal.     This  operation 
requires  much  care  and  attention  on  the  part  of  the  workmen. 

(7)  The  plates  are  scoured  with  sand,  under  water,  and 
are  left  under  clean  water  (or  sometimes  under  lime-water), 
which  hinders  rusting,  until  they  are  required. 


146       Metals :  their  Properties  and  Treatment. 

(8)  The  brightened  plates  are  rubbed  with  bran  in  order 
to  dry  them,  and  the  drying  is  completed  by  leaving  them 
for  an  hour  in  a  cast-iron  pot  filled  with  melted  tallow. 

The  process  employed  in  some  modern  tin-plate  works 
for  preparing  the  plates  to  be  tinned  is  much  simpler  than 
that  just  described. 

(1)  They  are  pickled  in  warm  diluted  sulphuric  acid  for 
about  twenty  minutes,  which  dissolves  the  black  oxide  -of 
iron  from  the  surface,  the  cleansing  being   completed  by 
scouring  them  with  sand  and  water. 

(2)  The  plates  are  annealed  by  being  heated  to  redness, 
for  twelve  hours,  in  an  air-tight  cast-iron  box  capable  of  con 
taining  i, 800  of  them,  placed  in  a  reverberatory  furnace ;  they 
are  allowed  to  remain  in  the  box  till  quite  cold,  when  they 
are  found  to  have  acquired  a  deep  purple  colour,  from  a  thin 
coating  of  oxide. 

(3)  They  are  cold  rolled  between  very  hard  polished  rollers, 
so  as  to  toughen  them. 

(4)  They  are  annealed  as  before  for  about  six  hours. 

(5)  The  plates  are  again  immersed  for  ten  minutes  in 
warm  sulphuric  acid,  weaker  than  that  employed  in  pro 
cess  i,  and  finally  scoured  with  wet  sand. 

Tinning. — (i)  In  order  to  tin  them,  they  are  transferred 
into  another  cast-iron  pot  containing  melted  tin  covered  with 
three  or  four  inches  of  tallow,  and  heated  over  a  fire  to 
nearly  the  inflaming  point  of  the  grease.  About  340  plates 
are  immersed  at  once,  and  are  allowed  to  remain  in  the  tin 
for  an  hour  and  a  half,  or  even  longer,  according  to  their 
thickness,  after  which  the  superfluous  tin  is  allowed  to  drain 
off  by  placing  them  upon  an  iron  grating. 

In  this  operation  of  tinning,  an  alloy  of  iron  with  tin  is 
formed  upon  the  surface  of  the  plate,  and  a  firm  adhesion  of 
the  tin  coating  is  thus  secured. 

(2)  The  next  operation,  washing,  is  intended  to  equalise 
the  coating  of  tin,  and  to  give  the  plate  a  smooth  bright 


Manufacture  of  Tin  Plate.  147 

surface.  For  this  purpose,  an  iron  pot  with  two  compart 
ments  is  employed,  both  of  which  are  filled  with  melted 
grain  tin,  of  high  purity,  one  being  designed  to  receive  the 
superfluous  tin  from  the  plate,  and  the  other  to  give  a  final 
coating  of  pure  tin.  The  plates  are  immersed  in  the  first 
compartment,  and  when  sufficiently  heated,  they  are  lifted 
out  by  tongs,  and  brushed  on  each  side  with  a  hempen  brush; 
they  are  then  dipped  for  a  moment  into  the  pure  tin  in  the 
second  compartment,  which  removes  the  marks  of  the  brush, 
and  afterwards  plunged  into  melted  tallow,  where  they  are 
left  for  a  certain  time,  and  at  a  particular  temperature,  in  an 
upright  position,  when  the  superfluous  tin  drains  down  to  the 
lower  edge  and  forms  a  rim  or  list  which  is  removed  in  the 
next  operation.  After  a  certain  number  of  plates  have  been 
dipped  into  the  first  division  of  the  washing  pot,  and  the  tin 
has  become  rather  impure,  about  3  cwt.  of  it  is  ladled  into  the 
first  tinning  pot,  and  replaced  by  an  equal  weight  of  grain  tin. 

(3)  The  plates  having  been  placed  in  another  vessel,  upon 
an  iron  grating,  to  cool,  their  lower  edges  are  dipped  into 
the  list-pot,  which  contains  a  layer  of  melted  tin  about  a 
quarter  of  an  inch  deep ;  as  soon  as  the  list  is  melted,  the 
plate  is  lifted  and  smartly  struck  with  a  stick,  when  the  rim 
of  tin  drops  off. 

After  the  grease  has  been  removed  by  rubbing  the  plates 
with  bran,  they  are  ready  to  be  packed  in  the  boxes,  which 
contain  100,  200,  or  225,  according  to  the  description  of 
plate.  About  |-  oz.  of  tin  is  sufficient  to  cover  a  plate  of 
iron  measuring  14  inches  by  10. 

Tin-plate  is  very  durable  as  long  as  the  coating  of  tin  is 
perfect,  but  if  any  portion  of  the  iron  surface  beneath  should 
be  exposed,  it  is  corroded  by  rusting  even  more  rapidly  than 
untinned  iron  plate,  because  the  iron  and  tin,  in  presence  of 
the  film  of  moisture  containing  carbonic  acid  which  is  de 
posited  by  the  atmosphere  upon  the  surface  of  the  plate, 
form  a  galvanic  pair  of  which  the  iron  is  the  metal  attacked 
by  the  water  and  acid,  so  that  the  plate  is  speedily  eaten 


148       Metals:  tJicir  Properties  and  Treatment. 

through.  In  the  manufacture  of  the  best  kind  of  tin-plate,, 
technically  termed  doubles,  and  popularly,  block-tin,  a  thicker 
coating  of  tin  is  given,  and  its  perfect  union  and  consolida 
tion  with  the  iron  plate  is  ensured  by  going  over  the  entire 
surface  with  a  polished  hammer  upon  a  polished  anvil,  an 
expenditure  of  manual  labour  which  of  course  greatly  in 
creases  the  cost  of  the  article. 

Tin-plate  moireed. — The  beautiful  variegated  appearance 
known  as  the  moire  metallique  is  produced  by  wiping  the 
surface  of  tin-plate  with  tow  or  sponge  dipped  in  a  warm 
mixture  of  diluted  nitric  acid  with  hydrochloric  acid,  or  with 
common  salt,  or  sal-ammoniac,  and  well  washing  with  water. 
The  acid  liquid  dissolves  away  the  smooth  surface  of  the 
tin  and  discloses  the  crystalline  structure  beneath,  the  varie 
gated  appearance  being  apparently  caused  by  the  reflection 
of  the  light  in  a  myriad  different  directions  by  the  minute 
faces  of  the  crystals.  The  moire  may  be  greatly  diversified 
by  heating  the  plate  before  applying  the  acid,  and  cooling  it 
irregularly  by  sprinkling  water  over  it,  or  by  directing  the 
blow-pipe  flame  over  its  surface  before  wetting  it  with  the 
acid.  The  surface  is  afterwards  covered  with  a  transparent 
coloured  varnish. 

Tinning  of  Copper. — Copper  saucepans,  stewpans,  &c., 
should  always  be  coated  with  tin,  since  most  kinds  of  food 
are  capable  of  dissolving  a  little  copper,  and  the  poisonous 
effect  of  the  compounds  of  this  metal  becomes  perceptible 
even  when  very  small  quantities  are  present.  Fortunately  it 
is  much  easier  to  tin  copper  than  iron.  The  copper  surface 
having  been  smoothed  by  rubbing  it  with  a  fine  sandstone,  is 
made  pretty  hot,  and  rubbed  over  with  powdered  sal-ammoniac, 
which  has  the  property  of  removing  the  oxide  from  the  sur 
face,  and  leaving  the  copper  perfectly  bright.  A  little  tin  is 
now  placed  upon  the  copper,  together  with  some  powdered 
rosin,  the  latter  being  intended  to  form  a  varnish  when  it  melts 
upon  the  surface  of  copper,  which  it  protects  from  being 
oxidised  by  the  air.  The  copper  plate  is  again  heated,  and 


Nature  of  A  Hoys.  1 49 

when  the  tin  melts,  it  is  spread  with  tow  over  the  surface,  to 
which  it  firmly  attaches  itself.  200  grains  of  tin  are  com 
monly  employed  to  cover  a  square  foot  of  copper.  The  tin 
employed  for  this  purpose  is  sometimes  alloyed  with  lead. 

ALLOYS  OF  TIN  AND  COPPER. 

The  term  alloy  (from  the  French  oilier,  to  blend  or  unite) 
is  applied  by  metallurgists  to  any  material  which  is  produced 
by  melting  two  or  more  metals  together.  The  properties  of 
the  metals  which  are  thus  alloyed  with  each  other  generally 
undergo  a  much  greater  alteration  than  can  be  accounted 
for,  if  it  be  supposed  that  the  alloy  is  a  mere  mechanical 
mixture  of  its  constituent  metals,  though  the  proportions  in 
which  metals  are  capable  of  being  alloyed  with  each  other 
are  not  so  fixed  and  definite  as  is  the  case  with  substances 
entering  into  chemical  combination  with  each  other.  Since, 
however,  chemists  are  able  to  produce,  in  some  cases,  very 
definite  chemical  combinations  of  one  metal  with  another,  it 
seems  probable  that  the  alloys  consist  usually  of  such  definite 
chemical  compounds,  dissolved  in,  or  mingled  with,  an  excess 
of  one  of  the  constituents  over  and  above  the  quantity  which 
is  actually  required  to  take  part  in  the  formation  of  a  chemi 
cal  compound. 

The  alloys  of  tin  and  copper  may  be  cited  in  illustration. 
When  two  parts  of  copper  are  melted  together  with  one  part 
of  tin,  the  mass,  after  cooling,  is  found  to  possess  properties 
very  different  from  those  of  either  of  the  metals,  being  very 
hard,  almost  as  brittle  as  glass,  and  having  a  white  silvery 
fracture.  No  merely  mechanical  mixture  of  two  soft  mal 
leable  metals  could  produce  one  which  would  be  hard  and 
brittle,  so  that  the  conclusion  appears  inevitable  that  a 
chemical  combination  has  taken  place  and  that  a  new 
material  has  been  produced.  The  tenacity  of  this  alloy  is 
only  about  one-fifth  that  of  tin,  and  one-fiftieth  that  of  copper, 
and  it  is  increased  by  the  addition  of  either  of  these  metals, 
which  appears  to  indicate  that  a  further  quantity  of  either  of 


150       Metals:  their  Properties  and  Treatment. 

them  merely  becomes  mixed  with  the  alloy.  When  this 
alloy  is  melted  with  more  copper,  it  is  entirely  dissolved  as 
long  as  the  metal  is  liquid,  but  during  the  cooling,  the  alloy 
tends  to  separate  into  two  parts,  one  containing  more  copper, 
which  solidifies  first,  and  the  other  much  richer  in  tin.  This 
result  would  indicate  that  the  original  alloy  had  not  formed 
a  true  chemical  combination  with  the  excess  of  copper,  but 
had  been  merely  dissolved  by  it. 

The  alloy  of  two  parts  of  copper  and  one  part  of  tin  forms 
the  basis  of  the  speculum  metal  of  which  the  mirrors  of  re 
flecting  telescopes  and  other  optical  instruments  are  made, 
arsenic  being  sometimes  added  in  the  proportion  of  about 
one-tenth  of  the  weight  of  the  tin,  in  order  to  harden  the 
alloy  and  render  it  susceptible  of  a  finer  polish.  A  little 
zinc  is  often  added  with  the  same  object.  In  order  to  make 
the  alloy,  the  copper  and  tin  are  melted  in  separate  crucibles, 
and  stirred  together  with  a  piece  of  wood.  Care  is  necessary 
in  employing  the  proper  proportions  of  the  metals,  for  an 
excess  of  tin  imparts  a  bluish  tinge  to  the  alloy. 

Bell-metal  is  an  alloy  of  copper  and  tin,  the  proportions 
of  which  are  varied  according  to  the  size  of  the  bells.  Large 
bells  are  cast  with  an  alloy  of  four  parts  of  copper  and  one 
part  of  tin,  which  is  also  the  composition  of  the  alloy  em 
ployed  for  cymbals  and  gongs.  The  metal,  when  first  cast, 
is  exceedingly  brittle,  but  it  becomes  somewhat  malleable 
after  being  heated  to  redness  and  quenched  in  water.  To 
give  it  the  elasticity  which  is  necessary  in  order  that  it  may 
emit  a  full  clear  sound,  the  bell  is  again  heated  and  allowed 
to  cool  slowly.  There  is  an  art  in  the  manufacture  of  a  good 
gong  which  appears  to  be  possessed  by  the  Chinese  alone, 
and  has  not  yet  been  successfully  imitated  in  this  country. 

Gun-metal  is  composed  of  90^  parts  of  copper  and  9^ 
parts  of  tin  ;  it  is  harder  and  more  fusible  than  copper,  and 
presents  great  resistance  to  any  strain  tending  to  force  its 
particles  asunder.  In  consequence  of  the  great  difference 
in  the  specific  gravities  of  the  metals,  it  would  scarcely  be 


Gun-metal — Casting  Bronze  Guns.  \  5 1 

possible  to  mix  them  thoroughly  if  they  were  simply  intro 
duced  together  into  the  reverberatory  furnace  in  which  the 
alloy  is  prepared.  It  is  customary,  therefore,  to  melt  the 
tin  first  with  twice  its  weight  of  copper,  so  as  to  obtain  hard 
metal,  which  is  then  added  to  the  proper  proportion  of  copper 
melted  on  the  hearth  of  the  reverberatory  furnace,  care  being 
taken  to  exclude  the  oxygen  of  the  air  from  the  hearth,  and 
to  mix  the  metals  thoroughly  by  stirring  them  with  a  wooden 
pole.  The  formation  of  the  alloy  is  facilitated  by  the  addi 
tion  of  some  old  gun-metal.  A  little  more  than  the  neces 
sary  proportion  of  tin  is  usually  added,  in  order  to  allow  for 
the  unavoidable  conversion  of  a  portion  of  that  metal  into 
oxide  by  the  oxygen  of  the  air.  When  the  metals  are 
thoroughly  mixed,  the  oxide  is  skimmed  from  the  surface, 
and  the  gun-metal  is  tapped  into  moulds  made  of  loam,  the 
stirring  being  continued  while  it  is  running,  to  counteract  the 
tendency  of  the  alloy  to  separate  into  two  parts,  as  above 
alluded  to.  For  the  same  reason,  the  alloy  is  run  into  the 
mould  at  a  temperature  as  little  as  possible  above  its  point 
of  solidification,  so  that  it  may  not  long  remain  liquid  in  the 
mould.  In  spite  of  these  precautions,  a  partial  separation  of 
the  metals  always  takes  place,  so  that  the  upper  portion  of 
the  casting  contains  more  tin  than  the  lower.  On  this 
account,  it  is  usual  to  cast  guns  with  their  muzzles  upwards, 
in  moulds  which  are  prolonged,  in  the  form  of  an  inverted 
truncated  cone,  to  about  three  feet  beyond  the  required 
casting  ;  the  excess  of  metal  forms  what  is  called  a  dead-head, 
the  weight  of  which  tends  to  prevent  the  separation  of  the 
metals  in  the  lower  part  of  the  casting.  This  dead-head 
exhibits  a  kind  of  ebullition  during  the  solidification,  and  a 
considerable  separation,  at  its  upper  part,  of  an  alloy  con 
taining  more  than  twice  as  much  tin  as  gun-metal.  The 
dead-heads  are  cut  off  before  the  guns  are  turned  and  bored, 
and  are  fused  in  the  furnace  where  the  gun-metal  is  prepared. 
When  the  white  alloy,  rich  in  tin,  separates  to  any  great  ex 
tent  in  the  lower  part  of  the  casting,  it  produces  flaws,  and 


152       Metals :  their  Properties  and  Treatment, 

the  gun  is  rejected.  Comparatively  few  bronze  guns  are  now- 
cast,  sinc.e  wrought  iron  and  steel  have  been  largely  em 
ployed  for  the  manufacture  of  ordnance,  being  much  lighter 
and  stronger. 

Bronze  has  essentially  much  the  same  composition  as  gun- 
metal,  but  great  variations  arevmade  in  the  proportions  of 
copper  and  tin,  in  order  to  adapt  it  for  special  purposes, 
small  quantities  of  lead  and  zinc  being  also  occasionally  added. 

The  bronze  coinage  of  this  country  contains  95  parts  of 
copper,  4  parts  of  tin,  and  i  part  of  zinc. 

The  effect  of  tin  in  hardening  copper  vvas  well  known  to 
the  ancients,  who  made  swords,  scythes,  nails,  &c.,  of  bronze, 
before  the  art  of  working  iron  and  steel  had  been  acquired. 
The  mode  of  tempering  such  bronze  weapons  was  just  the 
reverse  of  that  practised  with  steel,  the  bronze  being  rendered 
soft  and  somewhat  malleable  when  heated  and  quenched  in 
water,  but  hardened  again  by  being  heated  and  cooled  slowly. 

Tin  having  a  much  greater  attraction  for  oxygen  than 
copper  has,  a  considerable  proportion  of  the  former  metal  is 
lost,  as  oxide,  when  bronze  is  remelted. 

The  bronze-founder  employs  a  reverberatory  furnace  so 
arranged  as  to  prevent  access  of  air  to  the  metal.  By  the 
unskilful  remelting  of  old  bronze  guns,  the  tin  has  been 
reduced  to  less  than  half  the  original  proportion. 

Britannia-metal. — Tin  constitutes  the  chief  part  of  this 
and  some  similar  alloys  which  are  employed  for  the  manu 
facture  of  spoons,  tea-pots,  &c.,  being  hardened  for  such 
purposes  by  the  addition  of  antimony  and  copper.  Lead 
and  bismuth  are  also  sometimes  added. 

The  following  modifications  of  bronze  are  employed  for 
particular  purposes : — 

Wheel-boxes      Stop-cocks  and          Nails  for 
or  sockets          pump-valves      ships'  sheathing 

Copper  80  88  87 

Tin  .         18  10  9 

Zinc  ....          2  2  4 

100  100  100 


Occur  re)  ice  of  Zinc  in  Nature.  153 


ZINC. 

Metallic  zinc  is  not  met  with  in  nature,  and  though  its 
combinations  with  other  substances  are  abundant  in  certain 
localities,  they  are  by  no  means  universally  diffused  over  the 
earth's  surface.  England  is  not  particularly  rich  in  ores  of 
zinc,  and  the  extraction  of  the  metal  is  carried  out  in  this 
country  to  a  very  limited  extent,  most  of  the  zinc  required  in 
the  arts  being  imported  from  Silesia,  Belgium  and  Poland. 

The  ores  of  zinc  from  which  the  metal  is  extracted  are 
enumerated  in  the  following  table  :  — 

Ores  of  Zinc. 

Composition  Zincfin  IO°  Parts 

ol  pure  ore 

Blende       .         .         .         Zinc,  Sulphur  67 

Red  zinc  ore       .         .         Zinc,  Oxygen  80 


Calamine  .         .  xygen, 

ar 


Acid 

Blende  derives  its  name  from  the  German  blenden,  to 
dazzle,  in  allusion  to  its  lustre.  It  usually  occurs  in  black 
shining  crystals  which  owe  their  colour  to  the  presence  of 
sulphuret  of  iron,  since  the  pure  compound  of  zinc  with 
sulphur  is  white.  Blende  is  also  met  with  of  a  brown  or 
yellow  colour.  Black  blende  is  sometimes  regarded  as  a 
definite  compound  of  sulphuret  of  zinc  and  sulphuret  of 
iron,  containing  52  parts  of  zinc  in  the  hundred.  The 
chemical  name  of  blende  is  sulphide,  or  sulphuret,  of  zinc, 
and  the  miners  often  call  it  Blackjack.  It  is  found  running 
in  veins  through  limestone  or  sandstone,  and  is  commonly 
associated  with  galena  (sulphuret  of  lead)  and  with  iron  and 
copper  pyrites.  Blende  occurs  in  Cornwall,  Devonshire, 
Cumberland,  Derbyshire,  Ireland,  Wales,  and  the  Isle  of 
Man  \  also  at  Freiberg,  Aix-la-Chapelle,  and  in  North  America. 
It  sometimes  contains  a  considerable  proportion  of  cadmium, 

Red  Zinc  Ore  is  the  oxide  of  zinc,  which  would  be  white,  in 


£54       Metals:  their  Properties  and  Treatment. 

the  pure  state,  but  is  coloured  in  this  ore  by  the  oxides  of 
iron  and  manganese.  It  sometimes  forms  red  translucent 
prismatic  crystals,  and  is  found  chiefly  in  New  Jersey,  in  the 
United  States,  where  it  is  first  smelted  for  zinc,  and  after 
wards  for  white  pig-iron. 

Calamine  appears  to  be  so  called  in  allusion  to  the 
columnar  structure  of  some  specimens  of  the  ore,  which 
gives  them  some  resemblance  to  a  bundle  of  reeds  (calamus, 
a  reed}.  It  is  a  compound  of  the  oxide  of  zinc  with  carbonic 
acid,  which  would  be  white  if  pure,  but  is  usually  of  a  buff 
or  brown  colour,  due  to  the  presence  of  oxide  of  iron,  which 
is  objectionable,  because  it  corrodes  the  clay  vessels  em 
ployed  in  smelting  the  ore.  Calamine  occurs  in  veins, 
commonly  traversing  limestone  rocks,  and  is  associated  with 
blende,  galena,  and  electric  calamine,  which  resembles  cala- 
mine  in  appearance,  but  becomes  electric  when  heated. 
The  electric  calamine  is  a  compound  of  oxide  of  zinc, 
silica,  and  water  (hydrated  silicate  of  zinc),  and  though  it  is 
pretty  abundant  and  rich,  it  can  scarcely  be  regarded  as  an 
ore  of  zinc,  for  it  does  not  yield  its  zinc  in  the  ordinary 
process  for  extracting  the  metal.  Calamine  is  found  in 
Flintshire,  the  Mendip  Hills  in  Somersetshire,  Alston  Moor, 
in  Cumberland,  at  Lead  Hills  in  Scotland,  at  Aix-la-Chapelle, 
at  Tarnowitz  in  Silesia,  in  the  north-west  of  Spain,  and  in 
many  other  places.  It  sometimes  contains  more  than  two 
parts  of  cadmium  in  the  hundred.  In  Spain,  the  carbonate 
of  zinc  is  found  in  combination  with  the  hydrated  oxide 
of  zinc,  so  that  the  ore  contains  as  much  as  57  parts  of 
zinc  in  the  hundred.  Beds  of  calamine  are  reported  to  have 
been  recently  found  in  Sardinia. 

The  chief  English  zinc-works  are  situated  in  Birmingham 
and  Bristol,  where  the  ores  from  the  Mendip  Hills  and 
Flintshire  are  smelted ;  in  Sheffield,  where  the  ore  is  pro 
cured  from  Alston  Moor  ;  and  at  Swansea,  Wigan,  Llanelly, 
and  Wrexham. 

In  order  to  extract  zinc  from  its  ores,  advantage  is  taken 


Extraction  of  Zinc  from  its  Ores.  155 

of  the  comparative  facility  with  which  the  metal  is  converted 
into  vapour,  since  it  boils  and  distils  freely  at  a  temperature 
estimated  at  about  1900°  R,  a  bright  red  heat,  somewhat 
below  the  melting  point  of  copper.  The  ores  are  calcined 
so  as  to  obtain  the  zinc  in  the  form  of  oxide,  which  is  then 
mixed  with  carbon  and  distilled,  when  the  oxygen  passes  off 
in  combination  with  the  carbon  as  carbonic  oxide  gas,  and 
the  zinc  is  given  off  in  vapour  which  is  condensed  again. 
The  mode  in  which  the  operation  is  carried  out  differs  in 
different  works,  but  the  principle  of  the  process  is  always 
the  same. 

Calamine  is  the  principal  ore  treated  in  this  country,  and 
is  sometimes  smelted  without  previous  calcination,  because 
the  .carbonic  acid  which  is  combined  with  the  oxide  of  zinc 
can  be  driven  off  in  the  smelting  process  itself;  but  the  cal 
cination  or  roasting  of  blende  is  indispensable,  to  enable  the 
oxygen  of  the  air  to  convert  the  zinc  into  oxide,  and  to 
carry  off,  in  the  form  of  sulphurous  acid  gas,  the  sulphur 
previously  in  combination  with  the  metal.  Care  is  taken  to 
pick  out  as  much  of  the  galena  (sulphuret  of  lead)  as  pos 
sible,  because  the  oxide  of  lead  which  would  be  formed  from 
it  would  combine  with  the  silica  of  the  earthern  crucibles  em 
ployed  in  the  smelting  process,  and  would  seriously  corrode 
them.  The  blende  is  also  stamped  to  powder  and  washed 
to  free  it  from  earthy  matters  before  calcining. 

The  ore  having  been  broken  into  fragments  of  the  size  of 
a  nut,  the  calcination  or  roasting  is  effected,  as  usual,  by  the 
flame  of  a  coal  fire,  in  a  reverberatory  furnace  about  ten  feet 
long  and  eight  wide,  about  a  ton  of  ore  being  spread  upon 
the  hearth,  and  occasionally  raked  over.  The  roasting  is 
completed  in  10  or  12  hours. 

Blende  is  sometimes  subjected  to  a  preliminary  roasting 
in  heaps  (p.  19),  to  expel  a  part  of  the  sulphur  before  intro 
ducing  it  into  the  reverberatory  furnace. 

The  roasting-furnace  has  very  commonly  two  hearths,  one 
above  the  other,  so  that  the  flame,  having  traversed  the  sur- 


156       Metals:  their  Properties  and  Treatment. 

face  of  one,   must  pass  across  the  surface  of  the  second 
hearth  before  reaching  the  chimney.     The  ore  is  roasted  on 
the  upper  hearth,  which  has  the  lower  temperature,  for  1 2 
hours,  and  afterwards,  for  about  the  same  period,  upon  the 
lower  hearth.     At  Moriston,  near  Swansea,  the  roasting  fur 
nace  is  about  36  feet  long  and  9  feet  wide,  the  hearth  being 
divided  into  three  steps,  that  nearest  the  fire-bridge  being 
eight   inches  lower  than  that  near  the  chimney,  and  the 
middle  one  of  intermediate  height.     12  cwt.  of  blende  are 
roasted   for   eight  hours  on  the   coolest 
hearth  near  the  chimney,  then  for  eight 
hours  on  the  middle  hearth,  and  finally, 
for   a  similar  period,   upon   the   hottest 
hearth  near  the  fire-bridge,  fresh  charges 
having  been  introduced  at  the  other  end. 
In  order  to  save  the  clay  vessels  in 
which  the  distillation  is   effected,  those 
ores  which  contain  much  oxide  of  iron 
and  lime  are  mixed  with  others  contain 
ing  clay,  which  is  attacked  by  those  sub 
stances,   instead  of  the  material  of  the 
distilling  vessels. 

The  old  English  method  of  effecting 
the  distillation  is  now  almost  obsolete, 
either  the  Belgian  or  Silesian  process 
having  been  adopted  in  the  larger  zinc 
works,  but  the  process  is  sufficiently  interesting  to  merit  a 
short  description. 

Old  English  Method  of  Extracting  Zinc.—lte  roasted  ore 
is  distilled  with  coke  in  crucibles  (Fig.  54)  made  of  Belgian 
fire-clay  (nearly  pure  silicate  of  alumina),  furnished  at  the 
bottom  with  iron  pipes  in  which  the  zinc  is  condensed.  The 
crucibles  are  made,  generally  on  the  premises,  of  a  mixture 
of  equal  parts  of  fire-clay  and  old  crucibles  ground  to 
powder,  and  each  crucible  will  commonly  last  about  four 
months,  in  which  period  it  distils  two  tons  of  zinc.  The 


FIG.  54.— Crucible  for 
extraction  of  Zinc  by 
the  English  method. 


Extraction  of  Zinc  by  the  English  Process.     157 

crucibles  are  4  feet  high  and  2  j-  feet  wide,  and  the  iron 
pipes  which  pass  through  the  bottom  of  each  crucible  are 
seven  inches  wide.  These  pipes  are  made  in  two  pieces, 
the  shorter  length  being  cemented  into  the  bottom  of  the 
crucible,  and  the  other  (h\  about  eight  feet  long,  being  made 
to  fit  on  to  it  when  necessary.  Six  of  these  crucibles  are 


FIG.  55. — Extraction  of  Zinc  by  the  English  method. 

usually  set  in  one  furnace  (Fig.  55),  which  resembles  that 
used  in  a  glass-house,  having  a  long  grate  (a)  running 
through  the  centre,  on  which  a  brisk  coal  fire  is  maintained, 
the  flame  from  which  circulates  round  the  crucibles,  and 
issues  through  the  six  apertures  (d)  in  the  dome  (a).  The 
external  cone  (j)  serves  as  a  chimney  to  carry  off  the  smoke, 
and  as  a  jacket  to  retain  the  heat. 


158       Metals :  their  Properties  and  Treatment. 

The  pipe  at  the  bottom  having  been  loosely  plugged  with 
a  lump  of  coke  to  prevent  the  charge  from  passing  into  it, 
each  crucible  is  charged,  through  the  opening  (d)  above  it 
in  the  dome,  with  4  or  5  cwt.  of  the  calcined  ore  and  2  or 
3  cwt.  of  broken  coke  or  anthracite.  The  covers  are  then 
cemented  on  and  the  fire  applied.  In  a  short  time,  a  blue 
flame  appears  at  the  mouth  of  the  tube,  beneath  the  furnace, 
which  is  due  to  the  combustion  of  the  carbonic  oxide  formed 
by  the  combination  of  the  carbon  with  the  oxygen  of  the 
oxide  of  zinc.  After  a  few  hours,  the  flame  becomes  green 
ish  white,  from  the  combustion  of  the  vapour  of  zinc ;  it  is 
then  extinguished  by  attaching  the  longer  piece  of  iron  pipe, 
in  which  the  metal  condenses  and  drops  into  a  vessel  (g) 
containing  water ;  the  tube  (h)  is  removed  occasionally  in 
order  to  clear  out  the  zinc  which  obstructs  it.  The  distilla 
tion  occupies  about  sixty  hours,  and  the  ore  yields  rather 
more  than  a  third  of  its  weight  of  zinc,  a  considerable  pro 
portion  of  the  metal  being  still  left  in  the  form  of  electric 
calamine  (silicate  of  zinc)  which  cannot  be  made  to  yield  up 
its  metal  in  this  process. 

The  zinc  collected  in  the  receivers  is,  of  course,  not  in  the 
form  of  a  compact  mass  of  metal,  because  it  distilled  over  in 
separate  drops,  and  it  is  intermingled  with  a  considerable 
quantity  of  oxide  formed  as  the  heated  metal  dropped 
through  the  air  into  the  receiver.  It  is  therefore  remelted  in 
an  iron  pot  set  over  a  furnace,  and  well  skimmed,  the  dross 
being  introduced  into  the  crucibles  with  a  fresh  charge.  The 
zinc  is  cast  into  flat  cakes  or  ingots,  and  sent  into  commerce 
under  the  name  of  spelter* 

When  cadmium  is  present  in  the  zinc-ore,  it  passes  over 
in  vapour  before  the  zinc,  for  cadmium  boils  at  1580°  F., 
and  its  presence  is  indicated  by  the  brown  fumes  of  oxide  of 
cadmium  which  rise  from  the  flame  (brown  blaze).  The 
metal  which  then  distils  over  consists  of  zinc  containing  a 

*  The  name  spelter  is  also  given  to  an  alloy  of  equal  weights  of  zinc 
and  copper  employed  for  soldering  brass. 


Extraction  of  Zinc  by  the  Belgian  Process.      159 


large  proportion  of  cadmium,  and  is  collected  separately,  the 
cadmium  being  employed  in  making  a  particular  kind  of 
fusible  alloy  used  by  dentists,  whilst  its  compound  with 
sulphur  forms  a  yellow  paint  known  as  cadmia,  and  other  of 
its  combinations  are  useful  to  the  photographer. 

Extraction  of  Zinc  from  its  Ores  by  the  Belgian  Process. — 
This  process  is  now  that 
most  employed  in  England. 
The  distillation  of  the  mix 
ture  of  ore  and  coal  is 
effected  in  cylinders  which 
are  made  usually  in  the 
zinc- works  themselves,  from 
a  mixture  of  raw  and  hard- 
baked  fire-clay.  They  are 
about  8  inches  wide  and 
3  feet  long,  and  are  closed 
at  one  end.  A  large  num 
ber  of  these  cylinders,  vary 
ing  from  40  to  80,  are  ar 
ranged  in  tiers  (abed  Fig. 
56),  so  that  they  may  be 
heated  by  the  same  fire  (F), 
the  mouths  of  the  cylinders 
being  placed  a  little  lower 
than  the  closed  ends.  Two, 
or  even  four,  furnaces  are 
built  in  the  same  block, 
each  with  two  flues  running 
into  a  common  chimney, 
which  is  divided  into  four 
compartments,  each  having  a  separate  damper.  The  fur 
naces  near  Swansea  are  n  feet  wide,  9^  feet  high,  and  4  feet 
deep,  containing  78  cylinders. 

Coal  is  burnt  on  the  grate,  and  its  flame  penetrates  into 
the  furnace  through  four  openings  beneath  the  lowest  tier  of 


FIG.  56. — Belgian  Furnace  for  distilling 
Zinc  from  its  Ores. 


j  60      Metals  :  their  Properties  and  Treatment. 

cylinders.  Of  course  the  lower  cylinders  are  thus  raised  to. 
a  higher  temperature  than  the  upper  rows,  so  that  the  former 
are  charged  with  about  24  Ibs.  of  the  mixture  of  ore  and 
coal,  and  the  latter  with  16  Ibs.  Before  the  cylinders  are 
arranged  in  the  furnace,  the  interior  of  the  latter  is  gradually 
brought  to  a  high  temperature,  the  front  wall  being  tempo 
rarily  closed  in  for  that  purpose.  After  four  days,  the 
cylinders  are  set  in  their  places,  having  been  previously 
heated  to  redness  in  a  separate  furnace. 

The  mixture  of  ore  and  coal,  slightly  moistened  to  prevent 
dusting,  is  then  introduced  into  each  cylinder,  to  the  mouth 
of  which  is  then  cemented  a  conical  tube  of  fire-clay,  or  of 
cast  iron,  about  ten  inches  long.  In  a  short  time,  the  flame 
of  carbonic  oxide  gas,  formed  by  the  carbon  with  the  oxygen 
from  the  oxide  of  zinc,  is  perceived  at  the  mouth  of  the 
tube,  and  soon  afterwards  acquires  the  brilliant  greenish- 
white  appearance  which  indicates  that  the  zinc  is  beginning 
to  distil  over.  In  order  to  condense  the  vapours  of  zinc,  a 
conical  pipe  of  sheet  iron,  the  smaller  opening  of  which  is 
only  two-thirds  of  an  inch  in  diameter,  is  now  attached. 
After  the  lapse  of  two  hours,  this  is  removed  and  cleared 
out,  the  mixture  of  zinc  and  oxide  of  zinc  which  it  contains 
being  worked  again  with  the  next  charge.  The  bulk  of  the 
zinc  has  condensed  in  the  cast-iron  cones,  which  are  placed 
in  such  a  position  that  the  melted  zinc  remains  in  them,  and 
is  raked  out  by  the  workmen  into  a  large  iron  ladle.  The 
sheet-iron  cones  are  again  attached,  to  exclude  the  air, 
and  after  another  interval  of  two  hours  the  condensed  zinc  is 
raked  out  as  before.  Twelve  hours  are  required  to  distil  the 
zinc  from  a  single  charge  of  ore,  after  which  a  fresh  charge 
is  at  once  introduced,  so  that  the  furnaces  are  kept  in  con 
tinual  operation  for  two  months,  when  they  are  stopped  for 
repairs.  100  Ibs.  of  the  ore  furnish,  on  an  average,  31  Ibs. 
of  zinc,  but  a  considerable  proportion  of  zinc  still  remains, 
combined  with  silica,  in  the  residue,  since  the  extremely 
high  temperature  required  to  extract  it  would  soften  the  clay 


Extraction  of  Zinc  in  Silesia.  1 6 1 

cylinders  and  cause  them  to  collapse.  On  account  of  the 
high  price  of  coal,  clay,  and  labour,  ores  containing  less 
than  40  parts  of  zinc  in  the  hundred  cannot  be  worked  in 
Belgium. 

The  zinc  collected  in  the  iron  ladle  is  skimmed  from 
dross,  and  cast  into  ingots  weighing  from  70  to  80  Ibs.  each. 

At  the  Vieille-Montagne  works,  near  Aix-la-Chapelle,  the 
ore,  a  part  of  which  is  imported  from  Sweden,  consists  of  two 
kinds  of  calamine,  distinguished  as  white  ore  and  red  ore,  the 
latter  containing  more  iron  and  less  zinc  than  the  former. 
After  being  freed  from  clay  by  washing,  the  ore  is  calcined, 
efther  in  reverberatory  furnaces,  or  in  kilns  resembling 
lime-kilns,  in  which  coal  is  employed  as  fuel ;  it  loses  about 
one-fourth  of  its  weight.  The  ore  is  then  ground  to  a  fine 
powder,  sifted,  mixed  with  half  its  weight  of  coal-dust,  and 
distilled  in  the  furnace  described  above,  the  white  ore,  which 
is  richer  in  zinc,  being  introduced  into  the  lower  rows  of 
cylinders. 

Silesian  Process  for  Extracting  Zinc  from  its  Ores. — In 
Silesia,  ores  which  contain  only  1 8  or  20  parts  of  zinc  in  the 
hundred  are  worked  with  profit.  The  calcined  calamine  is 
distilled  with  coal  or  coke  in  large  muffles,  or  arched  ovens 
(Fig.  57),  3  or  4  feet  long,  by  8  inches  wide  and  18  or  20 
inches  high.  They  are  made  of  fire-clay  mixed  with  ground 
pots,  like  the  cylinders  employed  at  the  Vieille-Montagne, 
but  their  flat  bottoms  being  well  supported  throughout  their 
whole  length,  the  muffles  will  sustain  a  higher  temperature 
than  the  cylinders  without  bending,  so  that  the  distillation 
of  the  zinc  is  much  more  completely  effected.  The  calamine 
is  calcined  in  reverberatory  furnaces,  which  are  sometimes 
heated  by  the  waste  heat  of  the  smelting-furnace.  It  is 
broken  up  into  grains  about  as  large  as  a  pea,  mixed  with 
about  an  equal  bulk  of  broken  coke  or  fine  cinders,  and 
introduced  into  the  muffle  through  an  opening  which  is 
afterwards  closed  with  a  fire-clay  stopper.  The  muffles  are 
provided  with  rectangular  earthen  tubes,  prolonged  by  a 

M 


1 62      Metals :  their  Properties  and  Treatment. 

cast-iron  cone  and  a  sheet-iron  tube,  for  the  passage  and 
condensation  of  the  vapour  of  zinc,  an  opening  being  pro 
vided  through  which  the  tubes  may  be  cleared  from  obstruc 
tion.  Twenty  of  these  muffles  are  arranged  in  each  furnace, 
so  that  the  flame  may  pass  well  round  the  top  and  sides  of 
them,  and  the  firing  is  very  gradual,  to  avoid  all  risk  of 


FIG.  57. — Silesian  Zinc-furnace  ;  section.  /,  Arched  retorts,  y,  Door  for  re 
moving  the  exhausted  ore.  £,  Door  for  charging  the  retorts,  p  r,  Tube 
for  condensing  the  zinc,  b,  Receptacle  for  condensed  zinc. 


•u,  Fire-grate,     x,  Vaults. 


'.  k,  Flues. 


splitting  them.  The  condensed  zinc  drops  from  the  earthen 
tube  through  an  opening  corresponding  to  it,  in  the  fore- 
hearth  of  the  furnace,  and  is  collected  in  a  small  chamber 
beneath.  The  muffles  are  charged  afresh  every  24  hours, 
and  last  about  27  days.  The  residue  left  in  the  muffle  does 
not  retain  more  than  ^th  of  its  weight  of  zinc.  The  zinc 


Extraction  of  Zinc  in  Silesia.  163 

is  remelted  in  iron  pots  lined  with  clay,  since,  if  the  melted 
metal  be  in  direct  contact  with  the  iron  vessel,  the  latter  is 
corroded,  and  the  zinc  becomes  contaminated  with  iron, 
which  injures  its  quality. 

To  smelt  i  cwt.  of  zinc  from  the  ore,  the  coal  consumed 


FlG-    58  — Silesian  Zinc-furnace  ;   plan.      /,  Ai 
heating  the  retorts  before  setting  them  in 


Arched  retorts.      c,    Space   for 
---  -- »  - — "*  -n  the  furnace,     e,   Pot  for  re- 
melting  the  distilled  zinc,     i,  Iron  ingot-moulds  for  casting  the  zinc. 


is,  in  Belgium,  from  6  to  8  cwts.,  in  Silesia  from  10  to  15 
cwts.,  and  in  England  25  cwts. 

In  the  Belgian-Silesian  furnaces,  as  they  are  called  (Fig. 
60),  the  flame  is  made  to  pass  completely  round  the  muffles 
(a,  b\  and  to  descend  beneath  the  furnace  to  the  chimney. 
Thirty-two  muffles  are  commonly  arranged  in  each  furnace. 


M   2 


164       Metals :  their  Properties  and  Treatment. 

The  condensing-tubes  (,§)  have  a  depression  at  the  under 
side,  in  which  any  lead  which  distils  over  is  deposited,  and  the 
zinc  runs  off  in  a  purer  condition,  and  are  sometimes  pro 
vided  with  tapping-holes  through  which  the  zinc  may  be  run 
off  into  ingot-moulds. 

At  Stolberg,  a  furnace  of  this  construction  has  60  muffles 
arranged  in  two  tiers,  each  muffle  receiving  70  or  Solbs. 
of  ore. 

In  some  cases  it  has  been  found  economical  to  charge  the 
roasted  ore  into  a  cupola  or  small  blast-furnace,  in  alternate 


FIG.  59.— Silesian  Furnace  for  distilling  Zinc  from  its  Ores,     i,  Condensing  tube. 
/,  Openings  beneath  the  hearth  for  receiving  the  condensed  zinc. 

layers  with  fuel,  when  the  zinc  is  given  off  in  vapour,  which 
is  speedily  converted  into  oxide  by  the  oxygen  of  the  air, 
and,  being  collected  in  conden sing-flues,  is  distilled  in  the 
usual  way  with  coal  for  the  production  of  metallic  zinc. 
The  advantages  of  this  process  consist  in  the  greater  yield 
of  zinc  in  the  distillation,  and  the  absence  of  the  oxides  of 
lead  and  iron  which  do  so  much  damage  to  the  clay  vessels. 

At  Bleiberg,  the  zinc-dust,  or  mixture  of  finely-divided 
zinc  with  oxide  of  zinc  which  is  first  collected  during  the 
distillation  of  the  ores,  is  melted  in  fire-clay  tubes  set  up 
right  in  a  furnace ;  clay  pistons  attached  to  iron  rods  are 


Rolling  of  Zinc.  165 

thrust  into  the  tubes,  the  pressure  causing  the  finely-divided 
zinc  to  run  together,  so  that  it  may  be  tapped  out  from  the 
bottom  of  the  tubes.  The  metal  so  obtained  is  very  impure, 
containing  much  arsenic  and  cadmium,  which  always  pass 
over  with  the  first  portions  of  distilled  zinc. 


FIG.  60. — Belgian-Silesian  Zinc-furnace,  a  b,  Arched  retorts,  c  d,  Their 
supports,  f,  Flue,  g,  Condensing  tube,  h,  Receiver  suspended  by 
iron-wire,  k,  Fire-place. 

Rolling  of  Zinc  into  Sheets. — Before  the  year  1812,  zinc 
was  used  almost  exclusively  for  the  manufacture  of  brass, 
since  it  is  brittle  both  at  the  ordinary  temperature  and  at 
high  temperatures,  but  it  was  then  discovered  that  a  tem 
perature  between  200°  and  250°  F.  rendered  it  malleable 
and  capable  of  being  rolled  into  thin  sheets.  For  this 


1 66      Metals  :  their  Properties  and  Treatment. 

purpose,  however,  it  is  necessary  that  the  zinc  should  not 
contain  iron  or  lead,  the  former  of  which  it  acquires  when 
remelted  in  iron  pots,  while  the  lead  is  carried  over  in  the 
distillation  of  the  zinc,  in  consequence  of  the  presence  of 
galena  (sulphuret  of  lead)  in  the  ore. 

To  prepare  the  zinc  for  rolling,  the  ingots  of  spelter  are 
remelted  upon  the  fire-clay  hearth  of  a  reverberatory  furnace, 
which  is  made  to  slope  down  to  a  deep  cavity  or  sump  at 
one  end,  into  which  the  melted  zinc  flows.  Lead  (specific 
gravity  1 1  '4)  being  much  heavier  than  zinc  (specific  gravity 
6-9),  and  the  two  metals  having  very  little  disposition  to 
alloy  with  each  other,  the  bulk  of  the  lead  settles  down  to 
the  bottom  of  the  cavity,  so  that  the  upper  portion  of  the 
melted  metal  is  comparatively  free  from  lead.  It  is  then 
ladled  out  and  cast  into  ingots  of  convenient  size  for  rolling, 
and  after  these  have  been  again  heated  to  about  250°  F.  by 
the  waste  heat  of  the  furnace,  they  are  passed  between  cast- 
iron  rollers  and  reduced  to  the  required  degree  of  thinness. 

After  being  rolled,  the  zinc  always  retains  a  great  deal  of 
its  malleability,  even  after  cooling,  whereas  cast  zinc  may  be 
broken  by  laying  it  across  an  anvil  and  striking  it  with  a 
hammer.  The  fracture  of  an  ingot  of  zinc  presents  a  very 
beautiful  crystalline  appearance  and  great  lustre,  and  if  it 
contain  iron,  minute  grey  spots  are  visible  on  the  bright 
faces  of  the  crystals.  At  temperatures  above  400°  F.  zinc  is 
even  more  brittle  than  at  the  ordinary  temperature,  and  it 
may  be  obtained  in  extremely  fine  powder  by  pouring 
melted  zinc  into  an  iron  mortar,  and  well  stamping  it  with 
the  pestle  as  it  solidifies.  Powdered  zinc  has  been  employed 
as  a  metallic  paint  for  protecting  iron  from  rust. 

Since  the  discovery  of  the  malleability  of  zinc  at  very  high 
temperatures,  this  metal  has  been  extensively  employed  for 
gutters,  rain-pipes,  cisterns,  baths,  chimney-pots  and  roofing, 
purposes  for  which  it  is  eminently  fitted  by  its  lightness  and 
by  its  resistance  to  the  action  of  air  and  moisture;  for 
although  a  bright  surface  of  zinc  soon  tarnishes,  from  the 


Galvanised  Iron.  167 

formation  of  a  film  of  oxide  of  zinc  upon  it,  this  film  serves 
to  protect  the  metal  beneath  from  any  further  corrosion. 

An  objection  to  the  use  of  zinc  for  roofing  is  the  great 
combustibility  of  the  metal,  for,  at  a  red  heat,  it  takes  fire 
and  blazes  fiercely,  producing  light  white  flakes  of  oxide  of 
zinc,  which  is  used  as  a  paint,  under  the  name  of  zinc-white. 
In  casting  zinc,  it  is  important  to  avoid  employing  too 
high  a  temperature,  not  only  because  zinc  may  be  lost  in 
vapour,  but  because  burned  zinc  is  produced ;  that  is,  the  zinc 
becomes  very  much  harder,  and  difficult  to  cut  with  a  file 
or  chisel,  probably  because  it  has  dissolved  some  oxide  of 
zinc. 

Galvanised  Iron  is  sheet  iron  coated  with  zinc,  and  is 
made  in  a  similar  way  to  tin  plate,  by  thoroughly  cleansing 
the  surface  of  the  iron,  and  immersing  it  in  melted  zinc 
which  is  kept  covered  with  powdered  sal-ammoniac  (muriate 
or  hydrochlorate  of  ammonia),  this  salt  having  the  property 
of  dissolving  the  oxide  of  zinc  from  the  surface  of  the  bath. 
The  zinc  probably  alloys  with  the  iron  plate  to  a  slight 
depth.  A  small  quantity  of  iron  is  dissolved  by  the  melted 
zinc,  and  a  very  brittle  alloy  is  deposited  in  pasty  masses  at 
the  bottom  of  the  zinc-pot,  whence  it  is  removed  occasionally 
with  a  perforated  ladle.  This  alloy  has  been  found  to  con 
tain  6  parts  of  iron  and  94  parts  of  zinc.  In  some  large 
galvanised  iron  works,  where  much  of  this  alloy  is  obtained, 
the  zinc  is  recovered  by  distilling  the  alloy  in  clay  retorts 
like  those  employed  in  gas-works.  A  process  recently 
devised  for  treating  this  alloy  consists  in  melting  it  in  iron 
pots,  and  cooling  it  slowly,  from  the  bottom  upwards,  when 
an  alloy  of  9^-  parts  of  iron  with  90!  parts  of  zinc  is  de 
posited  in  crystals,  which  are  removed  by  a  perforated  ladle, 
and  the  liquid  zinc  is  left  much  purer.  The  crystallised 
alloy  is  distilled,  to  recover  the  zinc. 

The  zinc  coating  adheres  more  firmly  if  the  iron  is  pre 
viously  tinned.  Iron  articles  are  also  coated  with  zinc  by 
connecting  them  with  wires  attached  to  the  negative  pole  of 


1 68       Metals:  their  Properties  and  Treatment. 

a  weak  galvanic  battery,  and  immersing  them  in  a  solution 
of  sulphate  of  zinc ;  this  is  decomposed  by  the  galvanic 
current,  the  zinc  being  deposited  upon  the  surface  of  the 
iron,  which  is  thence  said  to  be  galvanised.  When  any  portion 
of  the  iron  surface  is  exposed  in  consequence  of  the  abrasion 
of  the  zinc,  the  adjacent  portion  of  the  latter  metal  will  pro 
tect  the  iron  from  corrosion,  because  the  two  metals  form  a 
galvanic  pair  of  which  the  zinc  only  is  attacked  by  the  mois 
ture  and  carbonic  acid  of  the  air.  It  will  be  remembered 
that,  in  the  case  of  tin  plate,  it  is  the  iron  which  is  the  metal 
attacked. 

Galvanised  iron  is  ill-adapted  for  situations  where  it  is 
much  exposed  to  the  acid  vapours  sent  into  the  air  by  some 
factories,  or  to  the  sulphuric  acid  found  among  the  products 
of  combustion  of  coal  and  gas,  because  zinc  is  among  the 
metals  most  easily  attacked  by  the  acids.  It  is  often  called 
corrugated  iron,  from  the  practice  of  ridging  and  furrowing 
the  plates  in  order  to  strengthen  them  for  building  purposes. 
Vessels  of  galvanised  iron  are  not  well  fitted  for  cooking 
utensils,  since  many  articles  of  food  are  liable  to  become 
contaminated  with  zinc  to  a  hurtful  extent. 

The  low  temperature  at  which  zinc  is  melted  (770°  F.), 
and  its  perfectly  liquid  condition,  recommend  it  for  casting 
statues,  since  it  runs  easily  into  the  very  finest  lines  of  the 
mould.  It  is  only  a  sixth  or  an  eighth  of  the  price  of 
bronze,  and  its  surface  can  be  coloured  so  as  to  resemble 
that  metal. 

ALLOYS  OF  ZINC  AND  COPPER. 

Brass  is  usually  described  as  an  alloy  of  zinc  with  twice 
its  weight  of  copper,  and  there  is  some  evidence  that  the 
metals  enter  into  a  true  chemical  combination  in  these  pro 
portions  ;  but  if  this  be  so,  the  compound  is  capable  of  dis 
solving  an  excess  of  either  metal,  the  proportions  employed 
for  brass  being  varied  to  suit  the  particular  purpose  for 
which  it  is  intended. 


Brass-founding. 


169 


Before  the  year  1780,  brass  was  always  made  by  strongly 
heating  copper  in  contact  with  calamine  and  charcoal  or 
coal.  3  parts  of  bean-shot  copper  (p.  129),  3  of  calcined 
calamine,  and  2  of  charcoal  were  heated  to  bright  redness 
in  a  covered  crucible,  when  the  zinc  reduced  from  the  cala 
mine  by  the  action  of  the  carbon,  instead  of  passing  off  in 
vapour,  as  in  the  extraction  of  zinc  from  the  ore,  entered 
into  combination  with  the  copper,  producing  brass  which 
was  found  in  a  melted  state  at  the  bottom  of  the  crucible. 
Brass  is  still  manufactured  by  this  process  at  Holywell  in 
North  Wales. 

When  metallic  zinc  is  employed  for  making  brass,  it  is 
usual  to  melt  the  zinc  in  a  crucible,  and  to  add  the  copper 
in  small  portions  at  a  time,  until  a 
nearly  solid  alloy  has  been  produced. 
This  is  broken  up  and  remelted  with 
the  proper  proportion  of  zinc. 

The  union  of  the  copper  and  zinc 
is  much  facilitated  by  melting  them 
with  old  brass.  Crucibles  made  of 
fire-clay,  or  of  a  mixture  of  fire-clay 
and  plumbago,  are  employed;  con-  FIG.  61.— Furnace  for  making 

j-  •  ,-    .  Brass.   #,  Arch  upon  which 

venient  dimensions  are  16  inches  in 
depth,  9!  inches  wide  at  the  mouth, 
and  6J  inches  at  the  bottom,  the 
sides  being  i  inch  thick,  and  the  bot 
tom  ii  inch.  Eight  of  these  crucibles  are  heated  by  a  single 
coal-fire  (Fig.  61),  the  flame  of  which  passes  up  and  circulates 
around  them,  and  afterwards  heats  two  empty  crucibles  placed 
above  them,  and  intended  for  the  subsequent  casting  of  the 
brass.  Suitable  proportions  of  the  metals  are  : 

41  Ibs.  of  old  brass. 

55  Ibs.  of  best  selected  bean-shot  copper. 

24  Ibs.  of  zinc. 

The  crucibles  are  filled  with  the  pieces  of  old  brass,  which 
are  melted  down,  and  leave  room  for  the  other  metals. 


apor 

the  crucibles  stand. 
Grate,  d,  Fire-door,  e, 
Damper,  f,  Inclined  plane 
for  carrying  away  cinders 
into  the  channel  g. 


1 70      Metals :  their  Properties  and  Treatment. 

Half  of  the  zinc  is  then  introduced,  in  small  lumps,  and 
covered  with  coal-dust ;  then  half  of  the  copper  and  another 
layer  of  coal-dust;  the  rest  of  the  metals  is  then  introduced 
in  the  same  way,  the  whole  covered  with  a  layer  of  coal-dust, 
and  the  crucibles  exposed  to  the  fire  for  about  four  hours, 
when  the  brass  is  ready  for  casting.  One  of  the  hot  empty 
crucibles  is  taken  out  of  the  furnace,  and  placed  in  another 
fire  so  as  to  keep  it  red-hot  whilst  four  of  the  crucibles  of 
brass  are  emptied  into  it ;  the  surface  is  then  skimmed,  and 
the  brass  is  poured  into  moulds  made  of  slabs  of  granite 
mounted  in  an  iron  frame,  the  joints  being  cemented  with  clay. 

The  presence  of  iron  in  brass  is  very  objectionable,  as 
it  gives  rise  to  deficient  tenacity  and  malleability. 

The  colour  of  the  alloy  of  zinc  and  copper  is  of  course 
dependent  upon  the  proportions  in  which  the  metals  are 
employed.  Those  alloys  which  contain  more  than  80  parts 
of  copper  in  the  hundred  exhibit  a  reddish  yellow  colour,  in 
which  the  red  predominates  as  the  quantity  of  copper 
increases,  the  colour  becoming  yellow  when  less  than  80  per 
cent,  of  copper  is  present.  If  the  amount  of  copper  be  less 
than  30  parts  in  the  hundred,  the  alloy  is  no  longer  yellow, 
but  approaches  more  nearly  to  the  colour  of  zinc. 

The  various  alloys  used  to  imitate  gold,  before  the  art  of 
electrogilding  was  introduced,  were  all  modifications  of  brass. 
Dutch  metal  or  Dutch  leaf  gold,  which  is  one  of  the  most 
malleable  of  alloys,  is  composed  of  n  parts  of  copper  and  2 
parts  of  zinc.  It  is  cast  into  thin  plates  between  slabs  of 
granite,  and  rolled  into  sheets,  being  occasionally  annealed 
(p.  5).  When  these  are  very  thin,  several  are  passed 
through  the  rolling-press  together,  and  they  are  eventually 
cut  up,  and  beaten  out  to  extreme  tenuity  in  piles  of  40  and 
80,  under  a  hammer  worked  by  water-power,  making  three 
or  four  hundred  strokes  per  minute.  Bronze-powder  (or  at 
least  one  kind  of  it),  used  for  decorative  purposes,  is  made 
by  reducing  the  thin  leaves  of  Dutch  metal  to  a  fine  powder. 
Such  powders  are  made  of  different  shades,  from  dark 


Varieties  of  Brass.  171 

copper  colour  to  pale  gold,  by  varying  the  proportion  of 
copper.  The  grinding  is  effected  with  a  very  little  oil,  to 
prevent  the  metal  from  being  tarnished  by  oxidation. 

Pinchbeck  is  composed  of  3  parts  of  copper  to  i  part  of 
zinc,  Princes  metal,  of  equal  weights  of  the  two  metals. 
Mosaic  gold  contains  about  equal  parts  of  copper  and  zinc. 
The  same  name  is  sometimes  applied  to  a  compound  of 
sulphur  with  tin. 

A  little  tin  is  added  to  the  brass  intended  for  engraving, 
since  it  causes  it  to  break  up  more  easily  under  the  action 
of  the  graver.  The  addition  of  a  little  lead  (about  3  oz.  to 
lolbs.)  much  facilitates  the  working  of  brass  at  the  lathe 
and  with  the  file,  since  it  prevents  the  shavings  and  filings 
from  greasing  or  adhering  to  the  tools. 

Brass  is  liable  to  be  rendered  very  brittle  when  placed  in 
situations  where  it  is  exposed  to  continual  vibration.  This 
seems  to  be  due  to  the  development  of  a  crystalline  struc 
ture  in  the  metal,  and  has  occasionally  caused  the  snapping 
of  the  suspending  chains  of  chandeliers. 

The  lacquering  of  brass,  in  order  to  protect  it  from  being 
tarnished  by  the  air,  consists  simply  in  varnishing  it  with 
shellac  dissolved  in  spirit  and  coloured  with  saffron,  annatto, 
dragon's  blood,  &c.,  so  as  to  give  it  a  golden  hue. 

Brass  is  bronzed  by  coating  it  with  a  thin  film  of  arsenic, 
mercury,  or  platinum,  the  last  being  used  only  for  small 
articles,  such  as  instruments,  on  account  of  its  high  price. 
A  solution  of  white  arsenic  (arsenious  acid)  in  muriatic 
(hydrochloric)  acid,  or  of  corrosive  sublimate  (chloride  of 
mercury)  in  vinegar,  is  brushed  over  the  brass,  previously 
warmed,  when  the  zinc  in  the  brass  chemically  displaces  the 
arsenic  or  the  mercury  from  the  liquid,  and  one  of  these 
metals  is  deposited  as  a  coating  upon  the  brass.  In  bronz 
ing  with  platinum,  a  solution  of  muriate  of  platina  (chloride 
of  platinum)  is  applied  in  a  similar  way.  There  is  much  art 
in  obtaining  a  durable  bronze  coating  of  any  desired  shade 
of  colour. 


172       Metals:  their  Properties  and  Treatment. 

Pins  which  are  made  of  brass  wire  are  tinned  by  boiling 
them  with  granulated  tin,  water,  and  cream  of  tartar  (bitar- 
trate  of  potash),  when  the  latter,  being  strongly  acid,  slowly 
dissolves  the  tin,  which  is  afterwards  displaced  from  the 
solution  and  deposited  upon  the  brass,  because  the  tin  and 
brass,  in  contact,  form  a  galvanic  couple,  which  decomposes 
the  salt  of  tin,  precipitating  that  metal  upon  the  surface  of 
the  brass  which  is  the  negative  plate  of  the  galvanic  pair. 

In  tinning  or  whitening  pins,  about  61bs.  of  pins  are 
spread  over  the  bottom  of  a  copper  vessel,  and  covered  with 
7  or  8  Ibs.  of  grain  tin ;  another  layer  of  pins  is  then  intro 
duced,  afterwards  more  tin,  and  so  on  until  the  vessel  is 
filled.  Water  is  then  poured  in,  the  vessel  heated,  and  \  Ib. 
of  cream  of  tartar  sprinkled  over  the  surface.  After  boiling 
for  an  hour  the  tinning  is  completed. 

Malleable  Brass  or  Muntz's  Metal,  or  Yellow  Sheathing. — 
This  is  an  alloy  of  3  parts  of  copper  and  2  parts  of  zinc, 
which  differs  from  common  brass  in  being  malleable  when 
hot.  It  is  of  course  cheaper  than  ordinary  brass,  on  account 
of  the  predominance  of  the  cheaper  zinc,  and  can  be  more 
easily  rolled  into  thin  sheets.  When  used  for  sheathing 
ships,  it  keeps  cleaner  than  copper.  A  small  proportion, 
less  than  T^th,  of  lead  is  now  commonly  added  to  Muntz's 
metal. 

The  nails  employed  for  securing  the  sheathing  contain,  in 
100  parts,  87  copper,  4  zinc,  and  9  tin,  the  latter  giving 
them  hardness. 

Aich  Metal,  or  Gedgts  Metal,  is  an  alloy  of  zinc  and 
copper  in  nearly  the  same  proportions  as  are  contained  in 
Muntz's  metal,  but  it  contains  also  a  little  iron.  It  consists, 
in  a  hundred  parts,  of 


Copper       .         .         60-0 
Zinc  .         .         .         38'2 


Iron    . 


This  remarkable  alloy  is  very  malleable  at  a  red  heat,  and 
may  be  hammered,  rolled,  or  drawn  into  wire,  with  the 
additional  advantage  of  being  readily  cast.  It  has  been 


German  Silver.  173 

employed  in  Austria  for  casting  cannon,  and  some  Chinese 
cannon  have  been  found  to  consist  of  a  similar  alloy. 

Sterro-metal*  is  another  very  strong  and  elastic  alloy  used 
by  Austrian  engineers  for  the  pumps  of  hydraulic  presses.  It 
contains  copper,  zinc,  iron  and  tin,  in  the  following  propor 
tions  in  a  hundred  parts,  the  proportions  varying  between 
the  assigned  limits  according  to  the  purpose  for  which  it  is 
required  : — 

Copper  .         .     55  to  60         I         Iron.         .         .     2  to  4 
Zinc        .         .     34  to  44         |         Tin  .         .         .     I  to  2 

Good  specimens  of  sterro-metal  have  been  found  to  offer 
far  more  resistance  than  gun-metal  to  transverse  fracture,  and 
it  is  only  two-thirds  of  the  price.  It  is  said  that  this  alloy 
was  accidentally  discovered  in  an  attempt  to  employ,  for  the 
manufacture  of  brass,  the  alloy  of  iron  and  zinc  found  at  the 
bottom  of  the  zinc-pots  in  making  galvanised  iron  (p.  167). 

A  very  hard  white  alloy  of  77  parts  of  zinc,  17  of  tin,  and 
6  of  copper  is  sometimes  employed  for  bearings  of  the  driving 
wheels  of  locomotives,  and  another  alloy  containing  90  of 
copper,  5  of  zinc,  and  5  of  antimony,  is  used  for  sockets  in 
which  the  steel  or  iron  pivots  of  machinery  are  to  work. 

German  Silver  or  Nickel  Silver. — The  metal  nickel, 
when  alloyed  with  copper,  whitens  it  more  than  a  similar 
quantity  of  zinc.  An  alloy  of  copper  with  a  quarter  of  its 
weight  of  nickel  has  a  silvery  white  colour,  and  is  sometimes 
called  nickel-silver.  But  the  ordinary  nickel-silver  of  com 
merce  contains  zinc  in  addition,  and  may  be  regarded  as 
brass  whitened  by  the  addition  of  nickel.  The  alloy  is 
somewhat  troublesome  to  make,  on  account  of  the  difficult 
fusibility  of  nickel.  One  method  of  making  German  silver 
consists  in  melting  the  copper  and  nickel  together  in  a 
crucible,  and  adding  the  zinc  in  pieces  previously  heated. 
According  to  another  process,  half  the  copper  is  placed  at 
the  bottom  of  the  crucible,  the  zinc  and  nickel  are  placed 

*  Named  from  the  Greek  adjective  strong,  firm. 


1 74       Metals :  their  Properties  and  Treatment. 

upon  it,  and  covered  with  the  remainder  of  the  copper.  The 
crucible  is  filled  up  with  charcoal-powder,  and  exposed  to  a 
strong  heat.  The  melted  metals  must  be  well  stirred  together 
with  an  earthenware  stirrer.  The  proportions  of  the  metals 
employed  in  making  German  silver  are  varied  according  to 
the  articles  required.  For  spoons  and  forks,  an  alloy  of  2 
parts  copper,  i  nickel,  and  i  zinc,  is  employed.  For  knife 
and  fork  handles,  5  copper,  2  nickel,  and  2  zinc.  For  rolling 
into  sheets,  3  copper,  i  nickel,  i  zinc.  For  castings  of 
German  silver,  3  parts  of  lead  are  added  to  100  parts  of  the 
alloy  first  mentioned.  The  larger  the  proportion  of  zinc,  the 
more  liable  is  the  German  silver  to  assume,  after  a  time,  the 
yellow  colour  which  is  so  objectionable. 

German  silver  was  originally  made  from  an  ore  containing 
copper,  nickel,  and  zinc,  found  at  Suhl  in  Germany. 

In  Nassau  an  alloy  of  copper  and  nickel  is  extracted  from 
a  complex  ore  consisting  of  copper  pyrites,  iron  pyrites, 
spathic  iron  ore,  haematite,  and  sulphuret  (sulphide)  of 
nickel.  The  treatment  of  the  ore  is  similar  in  principle  to 
the  Welsh  method  of  smelting  copper-ores,  except  that  the 
regulus,  corresponding  to  fine  metal  (p.  117),  which  con 
tains  both  the  copper  and  nickel,  is  completely  roasted  until 
all  the  sulphur  is  expelled,  and  both  metals  are  converted 
into  oxides  which  are  afterwards  reduced  to  the  metallic 
state  by  charcoal,  yielding  an  alloy  of  copper  with  about  half 
its  weight  of  nickel,  which  is  well  suited  for  the  manufacture 
of  German  silver. 

At  Mansfeld,  advantage  is  taken  of  the  chemical  attraction 
which  exists  between  nickel  and  arsenic,  to  separate  the 
nickel  from  its  ore  in  the  form  of  speiss,  which  is  a  semi- 
metallic  matt  composed  of  nickel  and  arsenic.  The  greater 
part  of  the  latter  is  separated  by  roasting,  which  also  converts 
the  nickel  into  an  oxide  ;  this  is  afterwards  treated  by  a 
purely  chemical  process  to  separate  the  rest  of  the  arsenic, 
and  the  oxide  of  nickel  is  eventually  reduced  to  the  metallic 
state  by  heating  it  with  carbonaceous  substances. 


Occurrence  of  L  ead  in  Nature.  175 

An  alloy  of  7  parts  of  copper  with  i  part  of  nickel  has 
been  employed  for  small  coinage  in  America. 

Aluminium-bronze  is  an  alloy  of  nine  parts  of  copper  and 
one  part  of  aluminium.  In  colour,  it  much  resembles  gold, 
but  is  much  harder  and  lighter.  It  is  extensively  used  as  a 
cheap  imitation  of  gold,  but  it  becomes  tarnished  in  course 
of  time.  It  has  also  been  employed  instead  of  steel  for  per 
forating  postage-stamps,  etc.,  and  is  said  not  to  be  so  soon 
blunted. 


LEAD. 

Whether  lead  in  the  metallic  state  has  ever  been  found  as 
a  true  natural  product  appears  to  be  doubtful,  since  the 
small  quantities  which  have  been  found  associated  with  the 
ores  of  lead  may  have  been  accidentally  reduced. 

Although  minerals  containing  lead  are  pretty  abundant, 
there  are  only  two  which  are  found  in  sufficient  quantity  to 
serve  as  sources  from  which  to  extract  the  metal  on  the  large 

scale. 

Ores  of  Lead. 


Galena  or                 ~\ 
Sulphuret  of  Lead  J     ' 

White  Lead  Ore  or  "1 
Carbonate  of  Lead  J 

Composition 
Lead,  Sulphur 

Lead,  Oxygen, 
Carbonic  Acid 

^ 
'  '  * 

Galena  is  by  far  the  most  abundant  of  the  compounds  of 
lead.  It  forms  extensive  veins,  traversing  clay  slate  in  Corn 
wall,  and  limestone  in  Derbyshire  and  Cumberland.  It  is 
also  found  in  Flintshire  (Holywell),  Scotland  (Leadhills), 
and  the  Isle  of  Man.  Spain  yields  abundance  of  galena  in 
Catalonia,  Grenada,  and  at  Linares  in  the  Sierra  Morena, 
where  it  occurs  in  granite.  This  ore  is  also  abundant  in  the 
Upper  Hartz,  at  Freiberg  in  Saxony,  and  in  the  United 


1 */6      Metals :  their  Properties  and  Treatment. 

States  of  America.  Few  ores  are  so  easily  recognised  at  once 
as  galena ;  it  is  distinguished  by  its  lustre,  which  is  almost 
metallic,  its  dark  grey  colour,  and  its  great  weight  (specific 
gravity,  7-5).  It  can  generally  be  easily  split  up  into  rect 
angular  fragments,  and  often  occurs  in  distinct  cubical 
crystals  of  large  size. 

Galena  almost  invariably  contains  silver,  which  takes  the 
place  of  a  part  of  the  lead  in  its  combination  with  sulphur, 
without  producing  any  alteration  in  the  crystalline  form  and 
general  appearance  of  the  ore.  A  galena  containing  two 
parts  of  silver  in  a  thousand  would  be  spoken  of  as  an  argen 
tiferous  galena*  because  even  that  small  proportion  of  metal 
can  be  profitably  extracted  from  the  lead  after  smelting  it 
from  the  ore. 

Antimony  is  also  found  in  many  specimens  of  galena,  as  a 
sulphuret  of  antimony,  and  its  presence  has  a  serious  influence 
upon  the  quality  of  the  lead  extracted  from  the  ore.  The 
minerals  commonly  associated  with  galena  in  the  vein  are 
blende  (sulphuret  of  zinc)  and  copper  pyrites,  whilst  cawk  or 
heavy  spar  (sulphate  of  barytes),  calc-spar  (carbonate  of 
lime),  and  fluor-spar  (fluoride  of  calcium)  are  often  found 
adjacent. 

White-lead  ore  or  carbonate  of  lead  is  a  much  less  important 
ore,  often  occurring  in  veins  of  galena,  and  apparently  pro 
duced  by  a  chemical  alteration  of  this  ore.  When  pure,  it  is 
a  white  crystalline  mineral,  but  it  has  often  an  earthy  appear 
ance,  and  it  is  so  unlike  galena  that  miners  have  been  known 
to  reject  it  as  worthless.  Sometimes  it  has  a  dark  colour, 
from  the  presence  of  a  little  galena  intermixed  with  it.  Car 
bonate  of  lead  is  found  in  considerable  quantity  near  Aix-la- 
Chapelle,  as  well  as  in  Spain,  and  in  the  valley  of  the 
Mississippi.  This  ore  is  so  seldom  smelted  apart  from 
galena,  that  it  is  not  necessary  to  describe  its  treatment 
separately. 

*  Argentum,  Latin  for  silver  ;  fero,  I  bear. 


Extraction  of  Lead  from  Galena.  177 

Sulphate  of  lead  (composed  of  lead,  sulphur,  and  oxygen), 
or  Anglesite,  is  very  rarely  found  in  any  quantity.  Australia 
furnishes  some  of  it,  containing  a  considerable  proportion  of 
silver. 

In  order  to  prepare  the  lead-ore  for  smelting,  it  is  sorted 
by  hand,  the  worthless  pieces  being  rejected,  and  broken  up, 
either  with  a  hammer  or  between  crushing-cylinders  ;  it  is 
then  washed,  in  much  the  same  way  as  the  ore  of  tin  (p.  131), 
in  order  to  separate,  as  far  as  possible,  the  foreign  matters 
mingled  with  it.  The  differences  in  the  ore  have  led  to  the 
adoption  of  different  methods  of  conducting  the  operation  of 
smelting;  thus  in  Derbyshire  and  Flintshire,  where  the 
lead  ores  are  rich  and  contain  very  little  quartz  (silica),  the 
galena  is  smelted  in  reverberatory  furnaces,  whilst  at  Alston 
Moor,  and  generally  in  the  lead-works  of  the  North,  small 
blast  furnaces  are  employed. 

Smelting  of  Galena  in  the  Reverberatory  Furnace. — The 
chemical  principles  upon  which  metallic  lead  is  separated 
from  galena  are  similar  to  those  involved  in  the  last  stage  of 
the  extraction  of  copper  (roasting  the  fine  metal  for  blistered 
copper,  p.  1 1 8),  the  sulphur  being  finally  expelled  in  the  form 
of  sulphurous  acid,  produced 'by  its  combination  with  oxygen 
previously  taken  up  from  the  air.  The  galena  is  first  roasted 
until  a  part  of  it  has  become  converted  into  oxide  of  lead, 
its  sulphur  having  combined  with  oxygen  and  been  removed 
as  sulphurous  acid. 

Galena 

^ Oxygen 

L^i Sulphur  from  the  air 

Oxide  of  Lead  Sulphurous  Acid  Gas 

Lead  Oxygen  Sulphur  Oxygen 

During  this  roasting  process,  another  portion  of  the  galena 
is  converted  by  the  oxygen  of  the  air  into  sulphate  of  lead. 

When  the  roasting  has  proceeded  far  enough,  the  oxide  of 
lead  and  sulphate  of  lead  are  melted  with  that  portion  of  the 


178      Metals:  tlitir  Properties  and  Treatment. 

galena  which  has  escaped  alteration,  when  the  whole  of  the 
sulphur  is  converted  into  sulphurous  acid,  and  the  lead  is 
left  in  the  metallic  state. 

Oxide  of  Lead 
Lead          Oxygen 


Galena 

Lead         Sulphur 
Sulphurous  Acid  Gas 


and 


give 


Sulphur 

Again — 


Oxygen 


and 


Galena 

Lead         Sulphur 

Sulphurous  Acid  Gas 

Sulphur  Oxygen 


and 


Lead 


Sulphate  of  Lead 


Lead    Sulphur    Oxygen 
and  Lead 


give 


FIG.  62.—  Reverberatory  Furnace  for  smelting  Galena. 


The  reverberator)'  furnace  in  which  the  smelting  of  galena 
is  effected  is  represented  in  Figs.  62,  63.  The  hearth  (B)  is 
about  eight  feet  by  six,  and  is  separated  from  the  grate  (F) 
by  a  fire-bridge  which  rises  to  about  eighteen  inches  from 
the  arch  (AA'),  the  latter  gradually  descending,  as  it  ap 
proaches  the  chimney,  until  it  is  within  about  six  inches  of 
the  hearth.  The  flame  and  products  of  combustion,  after 
passing  over  the  hearth,  are  conducted  by  two  openings  into 


Rcverberatory  Furnace  for  Lead  Ores.         179 

a  flue  about  eighteen  inches  wide  ;  this  flue  makes  a  bend 
downwards  towards  the  top,  and  is  carried  into  a  chimney 
between  fifty  and  sixty  feet  high.  The  flue  is  so  constructed 
that  it  may  be  readily  opened  to  clear  out  the  deposit  from 
the  lead  fumes.  The  fire-door,  for  throwing  the  coal  upon 
the  grate,  and  the  ash-pit  are  on  opposite  sides  of  the 
furnace  ;  that  upon  which  the  fire-door  is  situate  is  called 
the  labourer's  side,  whilst  that  opposite  is  the  working  side. 

On  the  labourer's  side,  there  are  three  openings  (o\  about 
six  inches  square,  at  equal  distances,  which  can  be  closed 
when  necessary  with  iron  plates.  There  are  three  corre- 


FIG.  63. — Plan  of  Reverberatory  Furnace  for  smelting  Galena. 

spending  openings  on  the  working  side  of  the  furnace,  as 
well  as  two  tapping-holes  for  the  lead  and  slag  respectively. 
The  hearth  of  the  furnace  is  lined  with  the  slags  from 
previous  operations,  which  are  spread  over  it  while  in  a 
pasty  state,  before  solidifying,  and  fashioned  to  the  proper 
shape  as  shown  in  Fig.  64.  On  the  labourer's  side,  it  is 
nearly  up  to  the  level  of  the  working  doors,  but  on  the  oppo 
site  side  it  is  hollowed  out  so  as  to  be  eighteen  inches  below 
the  middle  door ;  this  being  the  lowest  part  of  the  hearth, 
where  the  melted  lead  collects,  a  tap-hole  is  provided  for 
running  off  the  metal,  and  at  some  distance  above  it  is  the 
aperture  for  the  escape  of  the  slag.  Adjacent  to  the  tap- 

N    2 


1 80       Metals :  their  Properties  and  Treatment. 

hole  there  is  a  basin  outside  the  furnace  for  the  reception  of 
the  lead.  The  ores  are  selected,  if  possible,  so  that  the 
earthy  matters  associated  with  them  may  act  as  fluxes  to 
each  other  (p.  35),  or  else  some  lime  is  added  in  order  to 
combine  with  the  silica  and  form  a  fusible  slag. 

The  operation  of  smelting  galena  in  the  reverberatory 
furnace  consists  of  four  consecutive  stages,  distinguished  a? 
first,  second,  third,  and  fourth  fires. 

First  fire. — As  soon  as  the  lead  smelted  in  the  preceding 


FIG.  64.— Hearth  of  Reverberatory  Furnace  for  smelting  Galena. 


operation  has  been  tapped  into  the  outer  basin,  and  while 
the  furnace  is  still  glowing,  the  fresh  charge  of  about  a  ton 
of  ore  is  introduced  through  a  hopper  (T,  Fig.  62)  in  the 
arch  of  the  furnace.  No  regular  fire  is  made  up,  but  only  a 
little  coal  is  thrown  into  the  grate  to  keep  up  a  moderate 
temperature,  for  if  this  were  raised  too  high  at  first,  the 
galena  would  fuse,  and  the  roasting  would  be  rendered  im 
possible.  A  workman  stationed  at  the  labourer's  side 
spreads  the  ore  uniformly  over  the  surface  with  a  rake,  after 


Smelting  of  Galena.  1 8 1 

which  the  doors  are  closed  and  the  draught  moderated  by 
lowering  the  damper.  Since  there  is  little  fuel  upon  the 
grate,  a  considerable  quantity  of  unconsumed  oxygen  of  the 
air  passes  over  the  hearth  of  the  furnace,  so  that  some  oxide 
of  lead  and  sulphate  of  lead  are  soon  formed. 

After  the  roasting  has  been  continued  for  some  time,  the 
skimmings  from  the  lead,  run  into  the  outer  basin  at  the  end 
of  the  last  smelting,  are  thrown  into  the  hearth.  These 
skimmings  consist  chiefly  of  a  combination  of  lead  with  a 
small  quantity  of  sulphur  (subsulphuret  or  disulphuret  of 
lead),  which  is  speedily  acted  on  by  the  oxide  and  sulphate 
of  lead,  as  above  explained,  with  separation  of  metallic  lead 
which  runs  down  into  the  hollow,  and  is  drawn  out  through 
the  tap-hole  into  the  basin.  This  first. portion  of  lead  con 
tains  a  larger  proportion  of  silver  than  that  tapped  at  a  later 
period  of  the  process.  The  workman  occasionally  turns 
over  the  ore  to  expose  fresh  surfaces,  and,  if  necessary, 
throws  a  little  small  coal  upon  the  charge  to  prevent  the 
oxidation  from  being  carried  too  far.  About  an  hour  after 
the  commencement,  a  large  quantity  of  lead  is  run  off,  being 
chiefly  derived  from  the  action  of  the  skimmings  upon  the 
roasted  galena. 

After  an  hour  and  a  half  from  the  commencement,  all  the 
doors  are  thrown  open,  and  the  ore  is  well  turned  over  by 
two  workmen  placed  on  opposite  sides  of  the  furnace,  after 
which  the  doors  are  closed.  At  the  end  of  two  hours,  the 
first  fire  is  completed,  a  sufficient  proportion  of  the  galena 
having  been  converted  by  the  roasting  into  oxide  and  sul 
phate  of  lead. 

Second  fire.— The  damper  of  the  furnace  is  now  partly 
raised,  and  more  coal  is  thrown  into  the  grate,  so  as  to  bring 
the  temperature  up  to  a  bright  red  heat. 

The  sulphuret  of  lead  in  the  ore  now  acts  upon  the  oxide 
and  sulphate  formed  during  the  previous  roasting,  and  the 
melted  lead  begins  to  run  out  in  abundance.  The  workman 
stationed  on  the  working  side  thrusts  the  pasty  slags  out  of 


1 82       Metals:  their  Properties  and  Treatment. 

the  basin,  whilst  the  man  on  the  labourer's  side  spreads 
them  over  the  rest  of  the  hearth ;  a  little  quicklime  is  now 
thrown  in  to  assist  the  fluxing,  and  the  doors  are  left  open 
for  a  short  time  to  cool  the  hearth  a  little,  which  is  found  to 
facilitate  the  draining  out  of  the  lead,  probably  by  chilling 
and  partly  solidifying  the  slag.  Occasional  cooling  is  desi 
rable  also  for  converting  the  mass  into  a  pasty  condition,  for 
if  it  were  allowed  to  become  liquid,  the  unaltered  sulphuret 
of  lead  would  sink  to  the  bottom  instead  of  being  acted  on 
by  the  oxide  and  sulphate  of  lead.  The  time  occupied  by 
this  second  fire  is  about  an  hour. 

Third  fire. — The  doors  are  all  shut,  and  the  damper 
entirely  opened,  more  fuel  being  thrown  upon  the  grate  so 
as  to  raise  the  hearth  to  a  still  higher  temperature  for  about 
three  quarters  of  an  hour,  when  the  doors  are  again  opened, 
the  slags  spread  over  the  hearth,  and  a  fresh  quantity  of  lime 
thrown  upon  them.  The  lime  enters  into  combination  with 
any  silica  which  may  have  united  with  the  oxide  of  lead, 
and  sets  the  latter  free  to  act  upon  any  portions  of  un 
altered  sulphuret  of  lead.  The  lime  also  acts  advantage 
ously  by  diminishing  the  fusibility  of  the  mass  and  thus 
facilitating  the  contact  between  the  sulphuret  of  lead  and  the 
oxide.  This  third  fire  also  occupies  about  an  hour. 

Fourth  fire. — The  grate  is  again  charged  with  fuel  and  the 
doors  closed  for  about  three  quarters  of  an  hour,  the  furnace 
being  thus  raised  to  its  highest  temperature.  The  tap-hole 
is  then  opened  to  allow  the  lead  to  run  into  the  outer  basin 
(G,  Fig.  63),  and  some  lime  is  mixed  with  the  slags  in  order 
to  dry  up  or  partly  solidify  them,  when  they  are  raked  out 
through  the  openings  on  the  labourer's  side,  and  the  furnace 
is  ready  to  receive  a  fresh  charge  of  ore.  A  little  small  coal 
is  sometimes  thrown  upon  the  hearth  at  the  conclusion  of 
the  fourth  fire,  to  remove  the  oxygen  from  any  oxide  of  lead 
which  may  still  remain. 

The  iron  of  the  tools  employed  in  stirring  the  contents  of 
the  hearth  is  seriously  corroded  by  the  sulphur  in  the  ore. 


Smelting  of  Galena.  1 8  3 

The  whole  operation  of  smelting  in  the  reverberatory 
furnace  lasts  about  five  hours,  and  the  coal  consumed  is 
about  12  cwts.  for  every  ton  of  ore,  being  less  when  fluor 
spar  is  present  to  act  as  a  flux. 

The  lead  in  the  outer  basin  is  covered,  as  already  men 
tioned,  with  a  layer  of  subsulphuret  of  lead,  which  is  thrown 
in  during  the  first  fire  with  the  next  charge.  Logs  of  wet 
wood  are  sometimes  let  down  into  it,  as  in  the  case  of  tin, 
to  cause  ebullition  and  promote  the  separation  of  the  slags, 
before  the  lead  is  cast  into  pigs. 

The  slag  amounts  to  about  one-fourth  of  the  weight  of  the 
ore,  and  sometimes  contains  as  much  as  40  parts  of  lead  in 
the  hundred,  so  that  it  is  smelted  in  the  slag-hearth,  to  be 
described  hereafter. 

At  Bleiberg  in  Carinthia,  the  lead  is  extracted  from  galena 
by  a  process  much  resembling  that  just  described  ;  but 
wood  is  employed  as  fuel,  the  grate  being  at  the  side 
instead  of  at  the  end  of  the  hearth,  and  the  hearth  of  the 
furnace  is  a  single  inclined  plane,  allowing  the  reduced  lead 
to  flow  at  once  out  of  the  furnace.  The  first  portion  of  lead 
which  runs  out  is  known  as  virgin  lead,  and  is  purer  than  the 
pressed  lead  obtained  later  in  the  process  when  the  tempera 
ture  is  much  higher.  The  Carinthian  lead  (Villacher  lead, 
from  the  town  of  Villach)  is  in  high  repute  for  its  purity. 

In  Nassau,  a  furnace  more  nearly  resembling  the  English 
reverberatory  is  employed,  and  towards  the  end  of  the  pro 
cess,  some  green  wood  is  added  to  the  charge  upon  the 
hearth,  in  order  that  the  steam  and  gases  evolved  from^it 
may  agitate  and  mix  the  pasty  mass.  The  lead  collected  in 
the  basin  outside  the  furnace  is  stirred  with  wood  (like  tin, 
see  p.  139)  before  being  run  into  pigs. 

In  some  of  the  Continental  furnaces,  metallic  iron  is  added 
to  the  charge  in  order  to  combine  with  the  sulphur  in  the 
galena,  and  separate  the  lead  in  the  metallic  state. 

When  galena  containing  much  antimony  is  smelted  in  the 
reverberatory  furnace,  a  portion  of  the  oxide  of  lead  com- 


1 84       Metals :  their  Properties  and  Treatment. 

bines  with  the  oxide  of  antimony  to  form  a  compound 
which  can  only  be  decomposed  by  the  coal  at  a  very  high 
temperature,  so  that  the  first  portions  of  lead  obtained  are 
much  purer  from  antimony  than  those  at  the  end  of  the 
process. 

Smelting  of  Lead  Ore  in  the  Scotch  Furnace  or  Ore-hearth. 
— Since  this  is  a  blast  furnace,  it  is  found  advantageous  to 
roast  the  ore  before  smelting  it,  in  order  that  it  may  bv 
rendered  more  porous  and  may  offer  less  obstruction  to  the 
blast. 

The  ore  is  spread  over  the  hearth  of  a  reverberatory  fur 
nace,  not  unlike  that  employed  for  roasting  copper  ores 
(p.  109),  in  charges  of  about  half  a  ton,  and  roasted  at  a 
moderate  heat  for  about  eight  hours,  being  frequently  turned 
over  as  is  usual  in  roasting  operations.  Some  antimony  is 
thus  expelled  from  the  ore,  which  would  otherwise  harden 
the  lead ;  a  considerable  quantity  of  sulphur  also  burns  ofif. 
The  roasted  ore  is  raked  out  of  the  furnace  into  a  pit  filled 
with  water,  which  causes  it  to  fly  into  fragments  suitable  for 
charging  into  the  ore-hearth. 

The  ore-hearth  (Fig.  65)  is  a  small  square  forge  or  blast 
furnace  about  two  feet  high,  and  18  inches  by  12  internal 
area.  It  is  arched  over  at  the  top,  so  that  the  lead  fume  may 
be  conducted  into  a  long  flue,  sometimes  five  feet  high  and 
three  feet  wide,  in  which  a  large  quantity  of  oxide  of  lead 
and  sulphate  of  lead  is  deposited.  At  the  Allenheads 
works,  this  flue  is  carried  up  the  side  of  a  hill  for  three  miles 
before  it  terminates  in  the  chimney,  in  order  to  secure  per 
fect  deposition  of  the  lead  fume,  which  would  otherwise 
involve  very  considerable  waste  ;  for  although  lead  is  not, 
like  zinc,  a  metal  capable  of  being  distilled,  both  the  metal 
and  its  sulphuret,  when  heated  in  a  strong  current  of  air,  are 
liable  to  be  carried  off  in  the  form  of  vapours,  which  after 
wards  combine  with  oxygen  from  the  air,  and  are  deposited 
as  oxide  and  sulphate  in  the  flues ;  these  deposits  are 
afterwards  heated  in  the  calcining  furnace  till  they  can  be 


The  Ore  Hearth. 


185 


made  to  stick  together,  and  are  then  smelted  in  another  fur 
nace  called  the  slag-hearth.  A  rain  cJiambcr  is  often  pro 
vided,  in  which  the  condensation  of  the  fume  is  assisted  by 
water  ;  and  the  great  length  of  flue  renders  it  necessary  to 
assist  the  draught  by  large  exhausting  pumps. 

Since  a  very  moderate  temperature  is  required  in  this  fur 
nace,  the  sides  and  bottom  are  lined  with  cast-iron  plates, 
and  in  front  of  the  furnace,  where  there  is  an  opening  about 


\  K;.  65. — Scotch  Furnace  or  Ore-hearth  for  the  extraction  of  Lead. 

a  foot  high,  a  sloping  iron  plate  a  b  (work-stone]  is  fixed, 
upon  which  the  materials  can  be  raked  out  when  necessary, 
for  examination  and  manipulation  by  the  smelter.  The 
bottom  of  the  furnace,  upon  which  the  melted  lead  collects, 
is  about  4!  inches  below  the  upper  surface  of  this  iron  plate, 
in  the  edge  of  which  there  is  a  groove  cut,  near  to  the  side 
of  the  furnace,  through  which  the  melted  lead  may  run  when 
it  rises  to  a  sufficient  height,  into  a  gutter  which  conveys  it 


1 86       Metals :  their  Properties  and  Treatment. 

into  a  cast-iron  pot  (F)  heated  by  a  separate  fire,  and  called 
the  melting-pot. 

The  blast-pipe  enters  at  the  back  of  the  furnace,  about  1 1 
inches  from  the  bottom.  Peat  is  the  principal  fuel  employed 
in  the  furnace,  in  the  form  of  square  blocks,  with  which  the 
furnace  is  filled  at  the  commencement,  some  judgment  being 
required  in  their  arrangement,  and  the  fire  is  lighted  by 
placing  one  of  the  blocks,  already  kindled,  in  front  of  the 
blast-pipe,  when  the  combustion  soon  spreads  throughout 
the  furnace.  The  first  charge  introduced  into  the  ore-hearth 
does  not  consist  of  the  roasted  ore,  but  of  the  residue  from 
a  previous  smelting  operation,  which  is  called  browse,  and 
consists  of  partly  reduced  ore  mixed  up  with  cinders ;  before 
this  is  thrown  in,  a  little  coal  is  put  on  the  fire  to  raise  the 
temperature,  and  in  a  short  time  the  charge  is  raked  out  upon 
the  work-stone  in  front  of  the  furnace,  and  examined,  in  order 
that  \\\zgrey  slag,  a  shining  glassy  mass,  may  be  picked  out 
and  thrown  on  one  side.  This  grey  slag  contains  a  quantity 
of  silicate  of  lead,  with  silicate  of  lime,  &c.,  and  requires  a 
higher  temperature  for  the  extraction  of  its  lead  than  is 
attainable  in  this  furnace  ;  it  is  therefore  smelted  in  the  slag- 
hearth,  to  be  presently  noticed. 

The  browse  cleaned  from  slag  is  thrown  back  into  the  fur 
nace,  and  its  behaviour  observed  ;  should  it  appear  to  melt 
too  readily,  it  is  rendered  less  fusible  by  adding  a  little  lime, 
lest  it  should  run  down  to  the  bottom  of  the  furnace  with  the 
metallic  lead  ;  on  the  other  hand,  if  it  does  not  become  soft 
enough  to  permit  the  lead  to  separate,  lime  must  also  be 
added  to  soften  it.  These  apparently  opposite  effects  of  the 
addition  of  lime  will  be  intelligible  on  referring  to  the  re 
marks  upon  the  use  of  that  material  in  the  extraction  of  cast 
iron  (p.  35).  A  fresh  quantity  of  grey  slag  is  thus  foimetl, 
and  is  removed  by  the  workman. 

A  peat  is  now  placed  before  the  opening  of  the  blast- 
pipe,  in  order  to  prevent  any  dust  from  entering  it,  and  a 
quantity  of  roasted  ore  with  a  little  coal  is  thrown  in.  After 


The  Slag- Hearth.  187 

about  twenty  minutes,  the  charge  is  again  raked  out  on  to 
the  work-stone,  the  grey  slag  picked  out,  the  remainder 
thrown  back  into  the  furnace,  and  a  fresh  charge  of  roasted 
ore  and  coal  added. 

These  operations  are  repeated  during  14  or  15  hours,  in 
which  period  one  or  two  tons  of  lead  will  have  collected  in 
the  outer  basin,  according  to  the  richness  of  the  ore,  and 
the  proportion  (varying  from  TVth  to  -j-^-th  of  the  whole) 
which  has  been  removed  in  the  grey  slag. 

The  separation  of  the  metallic  lead  is  partly  due  to  the 
action  of  the  sulphuret  upon  the  sulphate  and  oxide  of  lead, 
as  explained  at  p.  178-,  and  partly  to  the  removal  of  oxygen 
from  the  oxide  by  the  carbon  of  the  fuel. 

The  lead  extracted  in  the  ore-hearth  is  purer  and  softer 
than  that  obtained  by  the  reverberatory  furnace,  the  tempe 
rature  being  so  low  that  the  other  metals  contained  in  the 
ore  are  not  reduced. 

Smelting  of  Slags,  &c.,  in  the  Slag-hearth. — In  this  opera 
tion  the  object  is  to  extract  as  much  of  the  lead  as  possible 
from  the  slags  and  other  residues,  without  reference  to  its 
purity,  by  the  employment  of  a  very  high  temperature,  so  as 
to  completely  liquefy  the  slag.  The  general  construction  of 
the  furnace  (Figs.  66,  67)  is  not  very  different  from  that  of 
the  ore-hearth,  but  it  is  larger,  being  3  feet  high,  and  26 
inches  by  22,  internal  area.  The  sides  are  built  of  sand 
stone,  in  order  to  resist  the  much  higher  temperature  of  this 
furnace.  The  bottom  (A)  of  the  furnace  consists  of  a  cast- 
iron  plate,  and  is  covered  with  a  layer,  about  16  inches 
thick,  of  porous  cinders  tightly  rammed  down,  which  serves 
as  a  strainer  to  separate  the  lead  from  the  slag,  since  the 
melted  metal  easily  percolates  into  the  porous  cinders, 
which  protect  it  from  being  oxydised  again  by  the  air,  and 
runs  thence  into  a  receptacle  (B)  outside  the  furnace,  which 
is  also  filled  up  with  similar  cinders,  and  has  an  opening 
through  which  the  lead  flows  into  an  iron  pot  (E)  kept  hot 
over  a  separate  fire.  The  slag  runs  off  the  surface  of  the 


iSS 


Metals  :  their  Properties  and  Treatment. 


layer  of  cinders,  both  in  the  furnace  and  in  the  receiving 
basin,  and  falls  into  a  cistern  of  water  (c),  where  it  breaks  up, 
so  that  the  lead  entangled  in  it  is  easily  separated  by  wash 
ing.  The  fire  is  lighted  with  peats  as  in  the  ore-hearth,  the 


FIG.  66.— Slag-hearth  lor  extracting  Lead. 

blast  being  forced  through  a  nozzle  at  the  "back  of  the 
furnace,  about  four  inches  above  the  layer  of  cinders.  Some 
coke  is  then  thrown  in,  and  about  six  hours  after,  when  the 
temperature  is  sufficiently  high,  a  charge  of  the  slags,  &c., 
which  are  to  be  smelted.  Coke  and  slags  are  thus  added  in 


FIG.  67.— Plan  of  Slag-hearth. 

alternate  charges,  as  in  the  iron  blast-furnace,  until  the  fur 
nace  requires  repair. 

The  charge  for  the  slag-hearth  commonly  consists  of: 
100  parts  of  slag  from  the  reverberatory  furnace; 
20       ,,       coal-ashes; 

13       ,,       clay-hearths  of  old  furnaces,  impregnated  with  lead  ; 
5       ,,       rich  slag  from  a  previous  operation" 


Economico  Furnace.  I  (89 

The  silica  and  alumina  present  in  the  clay  and  in  the 
coal-ashes  combine  with  the  lime  and  oxide  of  iron  in  the 
slag  from  the  reverberatory  furnaces,  and  form  an  easily- 
fusible  slag.  The  lead  is  reduced  to  the  metallic  state 
mainly  by  the  action  of  the  heated  carbon,  which  removes 
the  oxygen  from  the  oxide  of  lead.  The  coke  is  piled  up 
towards  the  front,  and  the  charge  towards  the  back  of  the 
furnace,  and  a  nose  or  prolongation  of  the  tuyere  is  allowed 
to  be  formed  by  the  solidified  slag,  so  as  to  carry  the  blast 
up  the  centre  of  the  furnace.  When  a  cold-blast  is  em 
ployed,  this  nose  is  apt  to  become  too  long,  so  that  air 
heated  to  about  300°  F.  is  found  to  answer  better,  beside 
effecting  a  considerable  saving  of  fuel.  If  the  blast  is  too 
hot,  the  slag  will  not  be  chilled  so  as  to  form  a  nose. 

A  very  inferior  description  of  lead  (slag-lead]  is  obtained 
from  the  slag-hearth. 

In  some  parts  of  Spain,  lead  is  extracted  from  the  slags  of 
the  Roman  lead-furnaces. 

Richardson's  Furnace,  or  the  Economico  Furnace,  which  is 
employed  in  Newcastle  and  the  neighbourhood  instead  of 
the  slag-hearth,  as  well  as  for  the  extraction  of  lead  from  the 
ore,  is  a  modification  of  the  Castilian  furnace  (Fig.  68),  being 
also  a  blast-furnace,  in  which  the  blast  is  either  supplied  by  a 
blowing-engine  through  three  tuyeres  or  blast-pipes,  or  is 
drawn  into  the  furnace  through  five  or  six  openings,  by  the 
action  of  a  tall  chimney.  The  body  of  the  furnace  is  circu 
lar  and  is  built  of  fire-brick,  about  8-J-  feet  high  and  2\  feet 
in  diameter,  the  bottom  being  lined  with  a  mixture  of  clay 
and  powdered  coke,  well  beaten  down,  and  hollowed  out  to 
receive  the  lead.  The  ore,  or  mixture  of  ore  and  slag, 
smelted  in  this  furnace,  must  not  contain  more  than  30  parts 
of  lead  in  the  hundred.  The  ore  is  roasted  previously  to  its 
introduction  into  the  furnace,  which  is  charged  with  ore  and 
fuel  through  an  opening  in  the  square  brick  structure  sup 
ported  on  four  pillars,  which  surmounts  the  furnace,  and,  if 
necessary,  the  charge  is  sprinkled  with  water  from  a  rose,  to 


FIG.  68.— Castilian  Furnace  for  Lead-smelting:.  A,  Body  of  the  furnace.  B,  Cru 
cible  for  receiving  the  lead,  c,  Blast-pipe.  D,  Masonry  enclosing  the  top 
of  the  furnace.  E,  Cast-iron  pillars.  F,  Receptacle  for  the  lead.  G,  Slot  for 
the  tapping-hole.  H,  Spout  for  overflow  of  slag.  I,  Charging-door.  ' 
r  Q,  Ground  line. 


Flue. 


Calcination  of  Hard  L  cad.  1 9 1 

prevent  the  dust  from  being  carried  into  the  flue.  The  slag 
flows  over  the  side  of  the  hearth,  as  in  an  iron  blast-furnace, 
into  cast-iron  waggons,  whilst  the  lead  accumulates  in  the 
cavity  at  the  bottom,  and  is  tapped  out  from  time  to  time 
into  an  iron  basin.  Limestone  is  sometimes  mixed  with  the 
charge,  to  flux  the  siliceous  matters. 

At  Clausthal  in  the  Hartz,  the  galena  is  reduced  by 
fusing  it  in  a  small  blast-furnace  or  cupola-furnace  with  granu 
lated  cast-iron,  which  combines  with  the  sulphur  to  form  a 
sulphuret  of  iron,  and  sets  the  lead  at  liberty.  The  sulphuret 
of  copper  which  is  present  in  the  ore  is  not  decomposed  in 
the  process,  but  forms  a  matt  upon  the  surface  of  the  lead, 
and  after  converting  the  sulphuret  of  iron  into  oxide  by 
roasting,  and  removing  the  oxide  by  fusion  with  siliceous 
matters,  the  sulphuret  of  copper  is  sent  to  the  copper 
smelting-works.  At  some  works,  slags  from  the  refining  of 
iron  (p.  52)  are  employed  to  assist  in  the  decomposition 
of  the  sulphuret  of  lead.  When  ores  in  a  finely  divided  state 
form  part  of  the  charge  of  the  slag-hearths  and  cupola  fur 
naces  on  the  Continent,  they  are  often  mixed  with  clay  or 
lime  and  moulded  into  bricks  before  being  thrown  into  the 
furnace. 

Softening  of  Lead  in  the  Calcining  or  Improving  Furnace. — 
The  lead  obtained  by  either  of  the  above  processes  some 
times  contains  considerable  quantities  of  silver,  antimony, 
copper,  and  iron,  which  harden  the  metal  and  render  it 
unsuitable  for  some  of  its  applications.  English  lead  is  the 
purest  which  is  to  be  found  in  commerce,  and  Spanish  lead 
is  the  most  impure  ;  the  composition  of  two  samples  in  100 
parts  is  here  contrasted  : 

English  Spanish        , 

Lead      .         .         ,  „  99-27  95-81 

Antimony       .         .  •'..  °'57  3^6 

Copper.         /•     ;  v  '•{,••  O'I2  0-32 

Iron       .    \\   .  K  [.'••'•  ;i  -  0-04  o-2i 

Even  the  English  specimen  is  sufficiently  impure  to  be 
designated  a  hard  lead. 


IQ2       Metals:  their  Properties  and  Treatment. 

When  the  lead  contains  any  notable  proportion  of  silvei, 
it  is  treated  by  a  special  process  to  be  described  hereafter, 
but  when  the  hardness  is  due  to  the  presence  of  antimony, 
&c.,  the  lead  is  softened  or  improved  by  exposing  the  melted 
metal  in  a  very  shallow  pan  to  the  action  of  the  oxygen  of 
the  air.  which  converts  the  antimony,  copper,  iron,  and  a 
considerable  portion  of  the  lead,  into  oxides,  which  collect  as 
a  dross  upon  the  surface,  and  are  skimmed  off  at  intervals, 
until  the  lead  is  found  to  be  sufficiently  softened. 

The  improving  furnace  (Figs.  69,  70)  is  a  reverberatory 
furnace  with  a  low  arch,  18  inches  above  the  hearth  near 
the  fire-bridge,  and  6  inches  near  the  chimney,  towards 
which  the  flame  is  drawn  by  two  flues  (F).  Since  a  large 


FIG.  69. — Calcining  Furnace  for  improving  Hard  Lead. 

spreading  flame  is  required,  the  fireplace  (D)  is  5  feet  long 
and  1 8  inches  wide,  being  divided  from  the  hearth  by  a  fire 
bridge  27  inches  wide  and  16  inches  above  the  hearth  (B). 
In  the  hearth  of  the  furnace  there  is  set,  with  a  space  round 
it  to  allow  for  expansion,  a  cast-iron  pan  measuring  10  feet  by 
5,  which  is  8  inches  deep  at  the  end  nearest  the  grate, 
and  9  inches  at  the  other  end  ;  at  this  deepest  end  there  is 
an  iron  gutter  (/)  stopped  up  during  the  process,  by  an  iron 
plug  with  a  weighted  lever  through  which  the  lead  may  be 
run  out  when  it  is  sufficiently  refined. 

Eight  or  ten  tons  of  the  hard  lead  are  melted  in  an  iron 
pot  (  .)  and  ladled  into  a  gutter  (H)  through  which  they  run 
into  the  improving  pan,  which  has  been  already  heated  to 


Improvement  of  Hard  Lead. 


193 


dull  redness  ;  the  gutter  is  then  closed  by  a  damper,  and 
the  improving  process  commences.  Its  duration  depends 
upon  the  amount  of  the  foreign  metals  (especially  of  anti 
mony)  which  the  lead  contains,  a  single  day's  calcination 
being  sufficient  to  soften  some  leads,  whilst  others  require 
two  or  three  weeks'  exposure  to  the  action  of  the  air  which 
passes  through  the  furnace.  The  dross  is  raked  off  occa 
sionally,  so  as  to  expose  the  surface  of  the  metal,  and  the 
progress  of  the  refining  is  observed  by  ladling  a  small  sample 
into  an  ingot-mould,  when  its  surface  assumes  a  peculiar 
crystalline  appearance  if  the  refining  is  completed.  The 


FIG.  70. — Plan  of  Improving  Furnace. 

refiner  also  judges  that  the  lead  is  sufficiently  softened,  if 
a  rainbow  or  iridescent  film  is  formed  upon  the  surface 
when  a  rake  is  pushed  over  it  from  the  working  door.  The 
softened  lead  should  not  form  round  globules  when  poured 
upon  a  heated  iron  plate. 

The  dross,  which  consists  chiefly  of  the  oxides  of  antimony 
and  lead,  is  mixed  with  coal  and  ground  under  edge-runners, 
previously  to  being  smelted  in  a  small  reverberatory  furnace, 
the  hearth  of  which  gradually  slopes  down  towards  the 
chimney,  where  there  is  a  cavity  for  the  reception  of  the 
metal,  which  constantly  flows  out  through  the  tap-hole  into 
an  iron  pot,  to  be  afterwards  transferred  to  the  pig-moulds. 


1 94       Metals:  tJicir  Properties  and  Treatment. 

The  hard  lead  thus  obtained  is  either  again  calcined  with  a 
fresh  portion  of  metal,  or  if  it  contains  a  very  large  propor 
tion  of  antimony  (of  which  some  specimens  contain  a  third 
of  their  weight),  it  is  sold  to  the  type-founders. 

The  process  of  improving  the  moderately  hard  lead  pro 
duced  at  Altenau  in  the  Upper  Hartz  resembles  the  boiling 
of  tin,  and  consists  in  melting  about  .11  tons  of  the  metal  in  an 
iron  pot  5  \  feet  deep  and  3  feet  wide,  and  stirring  it  for  two 
hours  with  a  birchen  pole  moved  by  machinery,  when  the 
violent  bubbling  of  the  gases  through  the  metal  continually 
renews  the  surface  in  contact  with  the  air,  causing  the 
formation  of  dross  containing  the  impurities. 

In  France,  the  improving  furnaces  often  have  two  fires, 
one  at  each  end  of  the  pan. 

Another  method  of  improving  very  hard  lead  consists  in 
melting  it,  as  above,  in  a  cast-iron  pan,  and  throwing  upon 
the  skimmed  surface  a  small  quantity  of  a  mixture  of  Peru 
vian  saltpetre  (nitrate  of  soda),  soda  and  lime,  the  addition 
being  repeated  until  the  metal  is  sufficiently  softened ;  the 
oxygen  of  the  saltpetre  converts  the  antimony  into  antimonic 
acid  which  combines  with  the  soda  and  lime,  and  is  removed 
as  dross,  together  with  a  considerable  quantity  of  oxide  of 
lead. 

Refining  of  Lead  containing  Silver  by  Pattinsoris  Process. — 
This  very  simple  and  beautiful  process,  which  was  introduced 
in  1829,  has  not  only  greatly  improved  the  quality  of  lead, 
but  has  very  much  increased  the  production  of  silver  in 
England;  previously  to  that  date  no  process  existed  by 
which  the  silver  could  be  removed  so  as  to  leave  the  lead  in 
the  metallic  state,  and  it  was  necessary  to  convert  the  whole 
.  of  the  lead  into  an  oxide  in  order  to  separate  the  silver,  this 
oxide  being  afterwards  smelted  to  recover  the  lead.  Since 
this  could  not  be  made  to  pay  unless  the  lead  contained  at 
least  eleven  ounces  of  silyer  in  the  ton,  any  smaller  quantity 
•  of  silver  was  left  in  the  lead  sent  into  the  market,  the  lead 
being  thereby  hardened,  and  the  silver  entirely  lost  for  all 


Pattinsons  Process.  195 

useful  purposes.  After  the  introduction  of  Pattinson's  pro 
cess,  much  of  the  old  lead  was  eagerly  bought  up  for  the 
sake  of  the  silver  which  it  contained. 

The  process  depends  upon  the  property  of  lead  to  crystal 
lise  at  a  lower  temperature  than  an  alloy  of  lead  and  silver, 
so  that  if  melted  lead  containing  a  small  proportion  of  silver 
be  allowed  to  cool  slowly  and  constantly  stirred,  the  small 
crystals  of  lead  which  are  formed  at  first  will  contain  little  or 
no  silver,  that  metal  remaining  in  the  liquid  portion. 

To  carry  out  this  principle,  a  series  of  melting-pots  is  em 
ployed.  The  number  of  pots  as  well  as  their  form  and 
general  arrangement  will  differ  somewhat  in  different  esta- 


FIG.  71.— Pots  for  desilverising  Lead. 

blishments,  but  for  the  sake  of  illustration,  a  desilverising 
plant  containing  five  pots  maybe  taken  (Fig.  71).  These 
pots  are  made  of  cast  iron  and  set  in  masonry ;  the  working- 
pots,  i,  2,  3,  and  4,  are  oval  in  shape,  their  mouths  being  40 
inches  by  26,  and  they  are  shaped  at  the  bottom  like  the 
small  end*  of  an  egg.  5  is  the  market-pot  for  melting  the 
desilverised  lead  before  casting  it  into  pigs ;  it  is  smaller 
than  the  others.  The  smallest  pots  (about  two  feet  in 
diameter),  between  i  and  2,  and  between  3  and  4,  are  the 
temper-pots,  for  containing  the  melted  lead  in  which  the 
perforated  ladle  (Fig.  72)  is  warmed,  which  is  used  for  fishing 
out  the  crystals  of  lead.  This  is  an  iron  ladle  about  18 
inches  wide  and  5  inches  deep,  with  an  iron  handle  of  4^ 

o  2 


1 96       Metals :  their  Properties  and  Treatment. 

feet  and  a  wooden  handle  of  about  5  feet  in  length  ;  the 
holes  in  the  ladle  are  \  inch  wide  and  f  inch  apart.  Each 
pot  is  heated  by  a  separate  fire. 

The  lead  to  be  refined  is  usually  in  pigs  (or  salmons] 
weighing  from  120  to  140  Ibs.  each.  About  64 
of  these  (or  4  tons)  are  melted  in  pot  i.  (See 
Fig.  73-)  When  they  are  perfectly  melted,  the 
fire  is  raked  out,  and  the  oxide  is  skimmed  from 
the  surface  of  the  lead.  In  order  to  hasten  the 
cooling  of  the  metal,  one  or  two  pigs  of  cold 
lead  are  thrown  in,  or  a  little  water  is  thrown 
upon  the  surface  so  as  to  form  a  solid  crust, 
which  is  then  pushed  down  into  the  liquid  metal. 
This  is  continued  until  crystals  of  lead  begin  to 
form. 

The  workman  then  detaches  any  lead  which 
has  solidified  on  the  sides  of  the  pot,  and  stirs 
the  melted  metal   with   an   iron   bar   in    order 
to   preserve  an   equal   temperature   throughout. 
Another  workman  takes  the  perforated  ladle  out 
II       of  the  temper-pot  in  which  it  has  been  heated, 
and  fishes  up  the  crystals  which  have  formed. 
The  handle  of  the  ladle  is  then  rested  upon  a 
pig  of  lead  faced  with  iron  placed  at  the  edge  of 
the  pot  to  serve  as  a  fulcrum,  and  the  workman 
seizes  the   end  of  the  long  handle,  and  jumps 
down  from  the  platform  around  the  pots  on  to 
the  floor,   thus  tilting  the  ladle  up  out  of  the 
melted  lead,  over  which  he  shakes  it  violently 
so  as  to  drain  all  the  liquid  metal  back  into  the 
pot.     The  ladle  is  then  swung  by  a  crane  over 
pot  2,  into  which  the  crystals  are  thrown ;  after 
this  has  been  repeated  for  an  hour,  only  about  one  ton  of 
lead  richer  in  silver  is  left  in  pot  i,  the  quantity  being  ascer 
tained  by  trying  the  depth  of  the  metal  in  the  pot. 

The  removal  of  the  crystals  is  still  proceeded  with,  but 


Pattinsoris  Process. 


197 


since  these  will  now  contain  too  much  silver  to  be  introduced 
into  pot  2,  they  are  thrown  upon  the  ground  in  order  to  be 
afterwards  melted  up  with  more  lead  in  pot  i.  When  only 
i  ton  of  the  rich  liquid  alloy  is  left  in  pot  i,  it  contains  about 
three  times  as  much  silver  as  the  original  lead,  and  is  ladled 
out  and  cast  into  eight  pigs,  which  often  contain  as  much  as 
150  ozs.  of  silver  in  the  ton,  together  with  any  copper  and 


FIG.  73. — Desilverising  Lead  by  Pattinson's  Process. 

antimony  which  were  contained  in  the  original  lead ;  whilst 
any  arsenic  which  was  present  will  have  passed  into  the 
crystals.  The  half-ton  of  crystals  which  have  been  thrown 
upon  the  ground  are  now  melted  in  pot  i  with  a  fresh  quan 
tity  of  the  original  lead,  and  treated  as  before. 

The  three  tons  of  crystals  of  lead  poor  in  silver  which 
were  transferred  to  pot  2,  are  made  up  to  four  tons  by  adding 


Metals :  their  Properties  and  Treatment. 

lead  of  the  same  richness  in  silver,  and  submitted  to  a  repe 
tition  of  the  same  treatment,  about  three-fourths  of  it  being 
transferred,  in  crystals,  to  pot  3,  one-eighth  of  it,  in  the  form 
of  richer  crystals,  being  thrown  upon-  the  ground  to  be  re- 
melted  in  pot  2,  and  the  remainder,  which  is  left  in  the 
liquid  state  at  the  bottom,  is  ladled  out  into  pot  i. 

The  crystals  in  pot  3  are  treated  in  the  same  way,  the 
portion  remaining  liquid  being  transferred  to  pot  2,  and  the 
poorer  crystals  melted  in  pot  4.  Finally  the  crystals  of  poor 
lead  formed  in  pot  4  are  ladled  into  pot  5,  to  be  cast  into 
pigs,  which  are  treated  again,  if  necessary,  until  the  silver  is  at 
last  reduced  to  half  an  ounce  in  the  ton.  By  a  single  operation 
in  the  four  pots,  as  just  described,  the  silver  in  the  market 
able  lead  is  reduced  to  one-tenth  of  its  original  amount. 

The  process  of  cupellation  for  extracting  the  silver  from 
the  rich  lead  is  described  under  Silver. 

The  quality  of  the  lead  is  greatly  improved  by  Pattinson's 
process,  not  only  because  the  bulk  of  the  antimony  and 
copper  remain  with  the  silver  in  the  liquid  portion,  but 
because  these  and  other  impurities  which  tend  to  harden  the 
lead  are  converted  into  dross  by  the  oxygen  of  the  air,  pre 
cisely  as  in  the  improving  or  calcining  process. 

The  description  just  given  refers  to  an  operation  with  Pat- 
tin  son's  process,  upon  the  low  system,  as  it  is  termed,  in  which 
-?ths  of  the  contents  of  each  pan  are  removed  in  crystals, 
whilst  according  to  the  high  system  only  f  rds  are  removed. 

The  high  system  is  preferred  for  the  treatment  of  the  leads 
richer  in  silver  and  of  otherwise  impure  quality,  as  many  as 
fifteen  pans  being  sometimes  employed,  so  that  there  is  a 
greater  chance  of  oxidising  the  impurities.  Both  systems 
are  combined  in  some  establishments,  in  order  to  suit  the 
different  descriptions  of  lead.  In  working  the  high  system, 
it  is  generally  found  that  the  crystals  taken  out  of  a  given 
pot  contain  about  half  as  much  silver  as  the  alloy  originally 
contained;  thus  nine  tons  of  a  silver-lead  containing  ten 
ounces  of  silver  to  the  ton  would  yield  six  tons  of  crystals 


Pattinsons  Process.  199 

containing  only  five  ounces  co  the  ton,  and  three  tons  of 
liquid  alloy  containing  twenty  ounces  to  the  ton. 

Where  many  pans  are  employed,  they  are  commonly 
hemispherical,  being  about  5  feet  wide  and  2\  feet  deep. 

If  the  lead  contains  as  much  as  60  ozs.  of  silver  in  the 
ton,  the  third  pan  is  selected  for  melting  it,  but  if  it  contains 
only  seven  ounces  in  the  ton,  it  is  melted  in  the  7th  pan,  an 
intermediate  pan  being  selected  in  other  cases. 

As  much  as  twelve  tons  of  lead  are  sometimes  melted,  to 
begin  with,  upon  the  high  system,  and  two-thirds  of  it  are 
ladled  out  in  crystals  into  the  next  left-hand  pan — an  opera 
tion  requiring  about  two  hours.  The  liquid  alloy  is  then 
chilled  into  a  pasty  condition  by  throwing  water  upon  it, 
and  ladled  out  into  the  next  right-hand  pan,  the  melting- 
pot  being  again  charged  with  twelve  tons  of  the  original 
lead ;  after  a  sufficient  quantity  of  metal  has  accumulated  in 
the  adjacent  pots,  the  crystallising  operation  is  repeated  with 
their  contents,  the  two-thirds  of  crystals  being  always  trans 
ferred  to  the  next  left-hand  pan,  and  the  one-third  of  liquid 
alloy  to  the  next  right-hand  pan.  Supposing,  therefore,  the 
rule  to  hold  good,  that  the  crystals  contain  half  as  much, 
and  the  liquid  twice  as  much  silver  as  the  silver-lead  from 
which  they  were  obtained,  the  lead  would  be  found,  after 
passing  through  four  pots  to  the  right  of  the  melting-pot,  to 
contain  sixteen  times  as  much  silver  as  the  original  lead, 
whilst,  after  it  had  passed  through  four  pots  to  the  left  of  the 
melting-pot,  it  would  contain  only  one-sixteenth  of  the 
original  proportion  of  silver,  as  indicated  below,  where  a 
lead  containing  seven  ounces  of  silver  in  the  ton  is  supposed 
to  have  been  melted  originally  in  pot  No.  7. 

No.  i.  No.  2.  No.  3.  No.  4.  No.  5.  No.  6. 

448  oz.         22402.          112  oz.          56  oz.  2802.  14  oz. 

per  ton.       per  ton.        per  ton.        per  ton.        per  ton.       per  ton. 

No.  7.  No.  £  No.  9.  No.  10.  No.  11 

7  oz.  3!  07.  if  oz.  |  oz.  T7S  oz 

per  ton.         per  ton.        per  ton.          per  ton.  per  ton. 


2OO       Metals :  their  Properties  and  Treatment. 

Instead  of  waiting  until  the  proper  quantity  of  metal  for 
crystallising  has  accumulated  in  a  given  pot,  the  right  com 
plement  of  a  sample  of  lead  of  the  richness  suitable  to  that 
pot  is  commonly  added  from  the  stock  kept  in  the  establish 
ment. 

Uses  of  Lead. — Many  of  the  uses  of  lead  result  from  its 
softness  and  plasticity,  properties  which  it  possesses  in  a 
higher  degree  than  any  other  metal  commonly  used  in  the 
metallic  state.  The  ease  with  which  it  may  be  rolled  into 
sheets  recommends  it  for  roofing  and  for  lining  sinks, 
cisterns,  &c.,  particularly  since  it  can  be  easily  adapted  to 
any  shape  with  the  aid  of  a  mallet.  Again,  its  softness 
enables  it  to  be  made  into  pipes  either  by  casting  a  very 
thick  cylinder  round  an  iron  core,  and  drawing  it  through 
progressively  diminishing  steel  dies,  or  by  forcing  the  melted 
metal,  by  hydraulic  pressure,  through  a  steel  cylinder  with  a 
core,  from  which  the  solidified  metal  issues  with  the  required 
form  and  dimensions. 

The  great  weight  of  the  metal  (specific  gravity  11*4)  is 
unfavourable  to  its  employment  for  roofing,  and  its  ready 
fusibility  (at  620°  F.)  is  another  disadvantage,  the  terrors  of 
a  conflagration  being  sometimes  aggravated  by  the  pouring 
down  of  the  melted  lead  from  the  roof. 

The  poisonous  nature  of  the  compounds  of  lead  renders 
it  dangerous  to  use  it  for  cisterns  and  pipes  with  which 
water,  and  especially  soft  water,  is  to  remain  in  contact  for 
any  considerable  period,  for  although  lead  itself  is  not  acted 
upon  by  water,  the  oxygen  of  the  air,  which  is  always  held 
in  solution  by  water,  readily  converts  a  portion  of  the  lead 
into  an  oxide  of  lead,  which  is  dissolved  in  small  quantity 
by  the  water  ;  even  if  a  very  minute  proportion  of  oxide  of 
lead  be  dissolved  in  the  water,  repeated  doses  of  it  will  give 
rise,  in  the  course  of  time,  to  the  most  painful  symptoms. 
Leaden  pipes  coated  internally  with  tin,  to  resist  the  action 
of  water  and  air,  are  made  by  drawing  out  two  concentric 
cylinders  of  lead  and  tin.  The  use  of  lead  in  connection 


A  Hoys  of  L  ead  and  A  ntimony.  2O I 

with  cider-vats  and  presses  is  highly  blameable,  for  the  lead 
is  dissolved  in  large  quantity  in  contact  with  the  acid  liquid, 
and  a  moderate  draught  of  such  cider  may  easily  contain  a 
poisonous  dose  of  the  metal. 

The  want  of  tenacity  exhibited  by  lead  prevents  it  from 
being  drawn  into  thin  wire. 

Its  softness  enables  lead  to  mark  paper,  which  rubs  off 
minute  particles  of  the  metal ;  the  pencils  in  use  for  metallic 
memorandum  books  are  composed  of  lead  hardened  by  the 
addition  of  tin  and  bismuth. 

The  easy  fusibility  of  lead  adapts  it  to  the  use  of  the 
type-founder,  but  it  is  far  too  soft  to  be  employed  alone  for 
this  purpose,  and  is  therefore  hardened  by  the  addition  of 
antimony. 

Type-metal  is  an  alloy  of  lead  with  one-third  or  one-fourth 
of  its  weight  of  antimony.  An  improved  description  of 
type-metal,  lately  introduced,  is  composed  of  two  parts  of 
lead,  one  part  of  tin,  and  one  of  antimony.  Another  alloy 
employed  for  the  same  purpose  contains  fifteen  parts  of  lead, 
one  part  of  tin,  and  four  parts  of  antimony. 

The  high  specific  gravity  as  well  as  the  fusibility  of  lead 
recommend  it  for  making  bullets  and  small  shot,  where  great 
momentum  is  required  in  a  small  compass.  Rifle  bullets 
must  be  made  of  very  pure  soft  lead  in  order  that  they  may 
easily  take  the  grooves  of  the  rifle,  and  the  iron  projectiles 
of  rifled  ordnance  are  coated  with  lead  for  a  similar  reason, 
but  a  somewhat  harder  lead  is  employed  here  ;  the  surface 
of  the  shot  or  shell  to  be  coated  is  thoroughly  cleansed, 
then  dipped  into  solution  of  sal-ammoniac,  and  afterwards 
into  melted  zinc,  the  coating  with  this  metal  being  found  to 
cause  a  firmer  adhesion  of  the  lead  into  which  the  missile  is 
next  plunged. 

Bullets  intended  to  be  discharged  from  smooth-bore  small 
arms,  especially  those  for  breech-loaders,  which  are  of  small 
size,  are  commonly  hardened  by  the  addition  of  one-fifth  of 
their  weight  of  antimony,  in  order  to  give  them  greater 


202       Metals :  their  Properties  and  Treatment. 

penetration.  The  bullets  employed  in  shrapnel  shells  are 
also  composed  of  four  parts  of  lead  and  one  part  of  antimony, 
partly  for  the  sake  of  penetration,  and  partly  that  they  may 
scatter  better,  bullets  of  soft  lead  being  liable  either  to  be 
jammed  together  by  the  force  of  the  explosion,  or  so  dis 
torted  as  to  make  a  very  short  flight  when  the  shell  bursts. 

Small  shot  for  fowling-pieces  are  composed  of  lead  con 
taining  from  three  to  six  parts  of  arsenic  in  a  thousand, 
which  has  the  effect,  not  only  of  hardening  the  lead  slightly, 
but  also  of  enabling  it  to  take  a  nearly  spherical  form  when 
the  melted  metal  is  dropped  through  a  colander  into  water. 
Another  condition  for  securing  spherical  shot  is  the  proper 
cooling  of  the  drops  before  they  fall  into  the  water,  for  if 
they  are  suddenly  chilled  and  solidified  externally  long 
before  the  inner  portion  solidifies,  the  shrinking  of  the 
latter,  as  it  cools,  causes  the  outer  layer  to  collapse,  and  the 
shot  becomes  deformed. 

Probably  the  effect  of  arsenic  in  securing  the  spherical 
shape  is  due  to  its  diminishing  the  contraction  of  the  still 
liquid  lead  as  it  cools  after  the  outer  portion  has  solidified. 

In  order  to  cool  the  drops  before  they  enter  the  water, 
they  are  commonly  allowed  to  fall  through  the  air  from  a 
considerable  height,  either  in  a  shot-tower,  or  in  the  disused 
shaft  of  a  mine  ;  or  the  same  object  is  sometimes  attained 
by  employing  a  rapid  blast  of  air,  when  a  high  fall  may  be 
dispensed  with.  The  larger  the  size  of  the  shot,  the  more 
preliminary  cooling  will  they  require,  so  that  large  shot  are 
allowed  to  fall  through  150  feet,  and  small  shot  through 
100  feet.  In  order  to  prepare  the  metal,  it  is  usual  to  alloy 
a  quantity  of  lead  with  a  large  amount  of  arsenic,  and  to 
add  this  to  melted  lead  in  the  proper  proportion.  A  ton  of 
soft  lead  is  melted  in  an  iron  pot,  and  40  Ibs.  of  arsenic 
added  to  it;  the  pot  is  covered  with  an  iron  lid,  and  the 
joints  cemented  with  clay  to  prevent  the  arsenical  vapour 
from  escaping  ;  the  metal  is  kept  melted  for  three  or  four 
hours,  then  carefully  skimmed,  and  cast  into  pigs.  The 


Uses  of  Lead.  203. 

arsenic  is  added  sometimes  in  the  metallic  state,  sometimes 
as  white  arsenic  (arsenious  acid,  composed  of  arsenic  and 
oxygen)  or  as  orpiment  (sulphuret  of  arsenic),  the  two  last 
being  decomposed  by  the  lead,  and  converting  a  portion  of 
that  metal  into  oxide  or  sulphuret.  Two  or  three  tons  of 
inferior  lead  having  been  melted,  five  or  six  pigs  of  the 
arsenical  lead  are  added,  and  well  stirred  up  with  it ;  a 
small  sample  is  allowed  to  fall  from  a  height,  through  a  per 
forated  ladle,  into  water;  if  the  drops  become  flattened,  too 
much  arsenic  has  been  added,  if  they  are  pear-shaped,  there 
is  too  little.  The  colantiers  are  wrought-iron  bowls  about 
10  inches  wide,  perforated  with  smooth  holes  varying  in 
size  with  the  description  of  shot  required.  In  order  some 
what  to  delay  the  passage  of  the  melted  lead  through  the 
holes,  the  colanders  are  lined  with  the  cream  or  scum  of 
oxide  which  forms  upon  the  surface  of  the  metal.  The 
temperature  of  the  lead  when  poured  into  the  colanders  is 
scarcely  adequate  to  scorch  straw.  The  drops  then  fall  from 
the  top  of  the  shot-tower  into  a  vessel  of  water  at  the 
bottom.  They  are  afterwards  dried  on  a  hot  plate,  sifted 
into  different  sizes,  the  deformed  shot  rejected  by  gently 
shaking  on  a  slightly  inclined  table,  when  only  the  spherical 
shot  roll  down,  and  these  are  polished  in  a  revolving  cask 
containing  a  little  plumbago. 

Lead  is  extensively  employed  in  the  construction  of 
vessels  for  various  chemical  manufactures,  since  it  resists 
the  action  of  sulphuric,  muriatic,  and  fluoric  acids  in  a  far 
higher  degree  than  iron,  copper,  zinc,  or  tin.  Even  nitric 
acid,  if  strong,  scarcely  attacks  lead,  though  the  diluted  acid 
readily  dissolves  it.  The  large  chambers  in  which  sulphu 
ric  acid  is  manufactured  are  built  of  leaden  plates  weighing 
5  or  6  Ibs.  per  square  foot.  Here  the  fusibility  of  the  metal 
becomes  an  advantage,  for  they  have  to  be  united  by  being 
burned  together,  that  is,  by  directing  a  hydrogen  flame  along 
the  edges  of  the  plates  so  as  to  unite  them  without  the  inter- 


204       Metals :  their  Properties  and  Treatment. 

vention  of  solder,  which  would  soon  be  corroded  under  the 
action  of  the  acid.  This  is  sometimes  called  autogenous 
soldering. 

Notwithstanding  that  lead  is  unacted  upon  in  the  cold  by 
strong  acids,  it  is  very  soon  extensively  corroded  when  ex 
posed  to  the  action  of  air  in  the  presence  of  carbonic  acid, 
and  becomes  eventually  converted  into  a  mass  of  white  lead  or 
(basic)  carbonate  of  lead.  Since  carbonic  acid  is  produced 
abundantly  by  the  decay  and  putrefaction  of  animal  and 
vegetable  matters,  metallic  lead  is  much  affected  when  kept 
in  contact  with  such  substances  in  the  presence  of  air,  the 
oxygen  of  which  unites  with  the  lead  to  produce  an  oxide  of 
lead  which  then  combines  with  the  carbonic  acid  and  forms 
a  carbonate.  The  lead  of  old  coffins  is  sometimes  found  to 
have  become  almost  entirely  converted  into  an  earthy-look 
ing  mass  of  white  lead  in  this  way,  a  very  thin  plate  of  lead 
remaining  in  the  centre.  The  oldest  process  for  the  manu 
facture  of  white  lead  depends  upon  the  corrosion  of  the  lead 
in  this  manner. 

In  breech-loading  cartridges,  where  grease  is  employed  as 
a  lubricator,  the  bullets  have  sometimes  become  partly  con 
verted  into  white  lead,  and  have  thus  increased  so  much  in 
bulk  as  to  burst  open  the  copper  case  of  the  cartridge  and 
render  it  useless. 

Alloys  of  Lead  and  Tin. — Pewter*  is  an  alloy  of  four  parts  of 
tin  with  one  part  of  lead;  it  is  harder,  possesses  more  tenacity, 
and  melts  more  easily  than  either  of  the  metals  separately, 
and  provided  that  the  lead  does  not  exceed  this  proportion, 
the  alloy  may  be  used  for  drinking-vessels  without  any 
danger  of  lead-poisoning.  Since,  however,  lead  is  far 
cheaper  than  tin,  a  larger  proportion  than  one-fifth  of  lead  is 
often  employed,  when  the  lead  is  apt  to  be  dissolved  if  left 
in  contact  with  the  acetic  acid  always  present  in  beer. 
Pewter  made  with  the  above  proportions  has  the  specific 

*  Probably  corrupted  from  the  French,  pottet  pot.  Potee  detain  is 
the  French  for  pewter. 


Soldering.  205 

gravity  7-8,  so  that  specimens  having  a  higher  specific  gra 
vity  than  this  will  be  known  to  contain  more  lead. 

The  solder  employed  by  the  pewterer  is  a  very  fusible 
alloy  of  tin,  lead,  and  bismuth.  The  solder  used  for  tin- 
plate  is  an  alloy  of  lead  and  tin.  Common  solder  contains 
equal  weights  of  the  two  metals  ;  fine  solder  contains  two 
parts  of  tin  and  one  of  lead  ;  coarse  solder,  two  parts  of  lead 
and  one  of  tin.  In  making  solder,  the  proportions  of  the 
metals  can  be  judged  of  from  the  appearance  of  the  alloy. 
When  it  contains  a  little  more  than  one-third  of  its  weight 
of  tin,  its  surface,  on  cooling,  exhibits  circular  spots  due  to  a 
partial  separation  of  the  metals  ;  but  these  disappear  when 
the  alloy  contains  two-thirds  of  its  weight  of  tin.  These 
alloys  melt  at  a  much  lower  temperature  than  either  of  their 
constituent  metals.  Common  solder  melts  at  385°  F. ;  fine 
solder  at  372°  F.,  whilst  the  melting-point  of  tin  is  442°  F., 
and  that  of  lead  is  620°  F. 

Soldering  is  scarcely  to  be  regarded  as  a  merely  mechani 
cal  adhesion,  but  depends  probably,  in  part,  upon  the  forma 
tion  of  an  alloy  between  the  solder  and  the  surface  of  the 
metal  to  be  soldered.  Hence  it  is  absolutely  necessary  that 
the  surfaces  to  be  united  by  the  intervention  of  solder  should 
be  perfectly  bright  and  free  from  oxide.  Several  substances 
are  employed  to  ensure  this  at  the  moment  of  applying  the 
solder;  one  of  the  commonest  is  muriatic  (hydrochloric) 
acid  killed  with  zinc,  that  is,  in  which  a  lump  of  zinc  has  been 
dissolved,  partly  with  the  object  of  saturating  a  portion  of 
the  acid,  partly  to  form  a  chloride  of  zinc  which  melts 
over  the  surface  of  the  work,  dissolving  any  oxide,  and 
protecting  the  metal  from  the  oxidising  action  of  the  air. 
Sal-ammoniac  (muriate  of  ammonia),  which  contains  hydro 
chloric  acid  combined  with  ammonia,  is  also  employed,  the 
hydrochloric  acid  removing  any  oxide  from  the  metallic 
surface;  sometimes  a  combination  of  sal-ammoniac  and 
chloride  of  zinc  is  used.  Rosin  in  powder  is  often  sprinkled 
over  the  metal  to  be  soldered,  when  the  heat  melts  it  and 


206       Metals :  their  Properties  and  Treatment. 

forms  a  varnish  to  protect  its  surface  from  the  oxygen  of  the 
air. 

Hard  soldering  or  brazing,  for  uniting  the  edges  of  iron, 
copper,  or  brass,  is  effected  with  an  alloy  of  brass  and  zinc 
made  by  adding  zinc  to  brass  melted  in  a  covered  crucible ; 
the  alloy  is  granulated  by  pouring  it  through  a  bundle  of 
twigs  held  over  a  tub  of  water,  and  before  being  used  for 
brazing  it  is  mixed  with  a  little  moistened  borax,  which 
'melts  when  the  heat  is  applied,  dissolving  off  any  oxide  from 
the  metals,  and  protecting  them  from  the  action  of  the  air. 
For  fine  work,  a  little  silver  is  added  to  the  alloy,  which  is 
thus  rendered  much  more  liquid  when  fused. 

Term-plate  resembles  ordinary  tin-plate,  but  is  coated  with 
an  alloy  of  tin  and  lead ;  it  is  largely  exported  to  Canada, 
where  it  is  employed  for  roofing. 


SILVER. 

This  metal  being,  in  general,  a  far  less  chemically  active 
metal  than  the  preceding,  that  is,  being  less  likely  to  enter 
into  and  remain  in  a  state  of  chemical  combination  with 
other  substances,  is  much  more  frequently  met  with  in  the 
metallic  or  native  state. 

Native  silver  has  generally  the  appearance  of  metallic 
twigs  and  branches,  which  are  sometimes  composed  of 
crystals  of  silver  strung  together.  The  silver-mines  of  Potosi 
exhibit  such  specimens.  Native  silver  is  also  found  at 
Kongsberg  in  Norway,  at  Andreasberg  in  the  Hartz,  Freiberg 
in  Saxony,  and  Schennitz  in  Hungary. 

The  native  metal  generally  contains  small  quantities  of 
gold  and  copper.  At  Kongsberg  a  yellow  alloy  is  found 
which  contains  silver  with  more  than  one-fifth  of  its  weight 
of  gold.  An  amalgam  of  silver  with  mercury  is  found  in 
large  quantity  in  the  silver-mines  of  Coquimbo,  Chili. 


Ores  of  Silver.  207 

Sulphuret  of  silver,  or  silver-glance,  containing,  in  its  pure 
state,  87  parts  of  silver  combined  with  13  of  sulphur,  is  one 
of  the  commonest  forms  of  combination  in  which  silver 
occurs  in  nature.  It  has  been  found,  in  a  pure  state,  in 
Cornwall,  Norway,  Hungary,  Saxony,  Bohemia,  Mexico, 
Peru  and  the  United  States.  It  has  a  slight  lustre,  and  a 
dark  grey  colour,  possessing  also,  which  is  remarkable  in  an 
ore  of  this  description,  a  good  deal  of  malleability  and 
flexibility,  and  it  is  so  soft  that  it  may  be  cut  with  a  knife. 
It  is  also  distinguished  by  its  fusibility,  being  easily  melted 
even  in  an  ordinary  flame. 

The  sulphuret  of  silver  is  more  abundant  in  association  with 
the  sulphurets  of  other  metals ;  thus,  in  argentiferous  galena, 
with  sulphuret  of  lead;  in  grey  copper  ore,  with  the  sulphurets 
of  copper,  antimony,  arsenic,  iron,  and  zinc ;  in  brittle  silver 
ore,  with  the  sulphurets  of  antimony,  iron,  and  copper  ;  in  red 
silver  ore,  with  sulphuret  of  antimony  or  sulphuret  of  arsenic. 
Blende,  iron  pyrites,  mispickel,  and  some  other  minerals 
sometimes  contain  a  minute  proportion  of  silver,  which  may 
be  extracted  with  profit,  incidentally  to  other  processes. 

Horn-silver  or  chloride  of  silver  contains,  when  pure,  7  5 
parts  of  silver  united  with  25  parts  of  chlorine.  Good 
specimens  of  this  ore  exhibit,  as  its  name  implies,  some 
resemblance  to  horn  in  appearance  and  softness.  It  is 
found  abundantly  in  Chili  and  Peru,  sometimes  in  large 
fragments,  but  more  commonly  in  very  small  cubical  crystals 
disseminated  in  a  ferruginous  rock. 

The  butter-milk  ore  of  the  German  miners  contains  chlo 
ride  of  silver  mixed  with  a  large  proportion  of  clay. 

Chloride  of  silver  has  been  found,  in  small  quantity,  in 
Cornwall.  Bromide  and  iodide  of  silver  are  also  found  in 
Mexico  and  Chili. 

In  consequence  of  the  high  price  of  silver,  it  admits  of 
being  extracted  with  profit  even  from  ores  which  contain  a 
very  small  proportion  of  the  metal,  especially  if  some  other 
useful  metal  can  be  extracted  at  the  same  time.  Thus, 


2C>8      Metals :  their  Properties  and  Treatment. 

silver  may  be  profitably  obtained  from  galena  containing 
only  two  parts  of  silver  in  a  thousand,  and  even  a  smaller 
quantity  than  this  is  extracted  from  some  copper  ores.  In 
these  cases,  the  lead  and  copper  respectively  are  extracted 
by  the  ordinary  smelting  processes,  and  are  then  subjected 
to  special  treatment  for  the  extraction  of  the  silver.  It  may 
be  well  to  describe  the  principal  methods  in  use  for  this 
purpose  before  considering  the  metallurgic  treatment  of  the 
ores  of  silver  with  the  sole  object  of  extracting  that  metal. 


FIG.  74. — English  Cupel  or  Test. 

Extraction  of  Silver  from  Lead  by  Cupetfatwn.—Host  of 
the  silver  produced  in  this  country  is  extracted  by  this 
process  from  the  rich  lead  obtained  in  Pattinson's  desilver- 
ising  process*  (p.  194)- 

The  process  of  cupellation,  which  is  one  of  the  most 
attractive  metallurgic  operations,  derives  its  name  either 
from  the  German  kuppel,  a  cupola  or  dome,  in  allusion  to  the 
shape  of  the  German  cupellation  furnace,  or  from  a  diminu 
tive  derived  from  the  Latin  cupa,  a  cup,  referring  to  the 
concave  hearth  upon  which  the  process  is  carried  out. 


Cupellation. 


209 


The  extraction  of  silver  from  lead  by  cupellation  depends 
upon  the  facility  with  which  the  latter  metal  is  converted 
into  an  oxide  by  the  action  of  air  at  a  high  temperature, 
whilst  silver  is  almost  entirely  unaffected ;  the  oxide  of  lead 
being  easily  melted,  is  partly  removed  from  the  surface  in  a 
liquid  state,  and  partly  absorbed  by  the  porous  hearth  upon 
which  the  silver  remains.  In  England,  this  hearth,  which  is 
called  the  cupel  or 
test,  is  an  oval  frame 
of  wrought  iron  (A, 
Fig.  74),  5  feet  long 
and  2\  feet  wide, 
which  is  crossed  by 
five  iron  bars  (a)  3j 
inches  in  breadth. 
This  frame  is  filled 
with  finely-powdered 
bone  ashes  mois 
tened  with  water,  in 
which  a  little  pearl- 
ash  (carbonate  of 
potash)  has  been 
dissolved ;  this  is  well 
consolidated  by  beat 
ing,  and  scooped  out 
until  it  is  about  f  of 
an  inch  thick  over 
the  cross  bars,  leav 
ing  a  flat  rim  of  bone- 
ash  all  round,  about  2  inches  wide,  except  at  one  end  (B),  the 
front  or  breast  of  the  cupel,  where  it  is  5  inches  wide  ; 
through  this  a  channel  (F)  is  cut,  to  allow  the  melted  oxide 
of  lead  to  flow  off  without  coming  in  contact  with  the 
iron,  which  it  would  corrode  very  'seriously.  This  cupel 
rests  upon  a  car,  in  order  that  it  may  be  wheeled  into 
its  place  under  the  reverberatory  furnace  (Fig.  75),  of  which 


FIG.  75. — English  Furnace  for  the  cupellation 
of  Lead. 


Metals:  their  Properties  and  Treatment. 

it  forms  the  hearth  (c),  where  it  is  arranged  so  that  the  flame 
of  a  coal  fire  (G)  passes  directly  across  it  to  the  two  flues, 
which  run  into  a  chimney  (B),  about  40  feet  high.  A  blast 
pipe  or  tuyere  (N)  enters  the  cupel  at  the  end  opposite  to 
that  through  which  the  oxide  of  lead  escapes,  and  throws  a 
blast  of  air  over  the  surface  of  the  metal  at  the  rate  of  about 
200  cubic  feet  per  minute.  Opposite  to  the  tuyere  is  a  hood 
with  a  pipe  (H)  for  carrying  the  fumes  into  the  chimney. 
The  cupel  is  very  gradually  heated  nearly  to  redness,  and 
almost  filled  with  the  lead  to  be  treated,  which  is  ladled  in 
from  an  iron  pot  (P),  in  which  it  has  been  previously  melted. 
From  500  to  600  Ibs.  of  lead  are  introduced  at  once.  In  a 
short  time,  the  surface  of  the  metal  becomes  covered  with 
oxide  of  lead,  or  litharge*  in  a  melted  state  ;  the  blast  is 
then  turned  on,  and  drives  the  litharge  in  wavelets  off  the 
surface,  through  the  channel  made  for  its  escape,  into  a  cast- 
iron  pot  outside  the  furnace.  When  this  channel  is  very 
much  corroded,  it  is  closed,  and  another  is  cut.  In  propor 
tion  as  the  lead  upon  the  hearth  diminishes,  fresh  portions 
are  ladled  in  from  the  melting-pot,  so  as  to  keep  the  lead  at 
about  the  same  level.  The  process  is  continued  for  sixteen  or 
eighteen  hours,  in  which  time  four  or  five  tons  of  lead  will  have 
been  added,  and  an  alloy  containing  about  eight  parts  of 
silver  in  a  hundred  will  be  left  in  the  cupel.  A  hole  is  then 
made  in  the  bottom,  through  which  the  metal  is  run  out  and 
cast  into  pigs.  A  fresh  charge  is  introduced  into  the  cupel, 
and  the  operation  continued  ;  one  cupel  will  often  last  for 
forty-eight  hours,  and  is  capable  of  treating  5  cwts.  of  lead 
per  hour,  with  a  consumption  of  i  cwt.  of  coal.  When  about 
3  tons  of  the  rich  alloy  (containing  8  per  cent  of  silver) 
have  been  obtained,  it  is  again  subjected  to  cupellation  in 
the  same  furnace,  but  in  a  cupel  which  has  a  concavity  at 
the  bottom  intended  for  the  reception  of  the  cake  of  silver, 
which  will  weigh  about  500  Ibs.  This  second  operation  is 

*  From  two  Greek  words,  signifying  stone  and  silver. 


Cupcllation.  2 1 1 

necessary,  because  the  litharge  which  is  formed  from  this 
very  rich  alloy  contains  a  considerable  proportion  of  silver, 
so  that  the  lead  obtained  by  smelting  it  (p.  212)  and  by 
smelting  the  cupel,  which  absorbs  a  large  proportion  of 
litharge,  contains  30  or  40  ozs.  of  silver  in  the  ton,  and 
must  be  treated  for  that  metal. 

The  appearance  of  the  metal  in  the  cupel  as  the  last  por 
tions  of  lead  are  removed  in  the  form  of  litharge  and  absorbed 
into  the  bone-ash,  is  very  beautiful.  When  the  film  of  oxide 
becomes  so  thin  that  the  bright  silver  beneath  can  reflect  the 
light  through  it,  a  decomposition  of  the  light  into  its  con 
stituent  colours  takes  place,  and  the  most  brilliant  rainbow 
tints  are  seen  upon  the  metal,  their  beauty  being  enhanced 
by  the  rapid  rotation  of  the  film.  As  soon  as  this  film  of 
oxide  has  been  absorbed  by  the  cupel,  the  splendid  surface 
of  the  melted  silver  shines  out  (figuration,  coruscation,  or 
brightening]. 

During  the  cooling  of  the  cake  of  silver,  some  very 
remarkable  phenomena  are  observed.  When  a  thin  crust  of 
metal  has  formed  upon  the  surface,  the  silver  beneath  it 
assumes  the  appearance  of  boiling,  and  the  crust  is  forced 
up  into  hollow  cones  about  an  inch  high,  through  which  the 
melted  silver  is  thrown  out  with  explosive  violence,  some  of 
it  being  splashed  against  the  arch  of  the  furnace,  and  some 
solidifying  into  most  fantastic  tree-like  forms  several  inches 
in  height.  This  behaviour  of  silver  has  been  shown  to  be 
due  to  its  property  of  absorbing  mechanically  (occluding) 
oxygen,  at  a  temperature  above  its  melting-point,  which  it 
gives  off  as  it  approaches  the  point  of  solidification,  the 
escaping  gas  forcing  up  the  crust  of  solid  silver  formed  upon 
the  surface. 

A  considerable  proportion  of  lead  and  silver  is  carried  off 
by  the  blast,  in  the  form  of  vapour,  and  is  partially  recovered 
as  oxide,  from  the  flues  of  the  furnace. 

In  some  cupellation  furnaces,  instead  of  employing  a 
blowing  machine,  a  current  of  air  is  directed  over  the  surface 

p  2 


212 


Metals :  their  Properties  and  Treatment. 


by  means  of  a  jet  of  steam  issuing  from  a  tube  surrounded 
by  a  wider  one  through  which  the  air  is  dragged  by  the 
mechanical  action  of  the  steam.  This  is  said  to  hasten  the 
operation,  and  to  produce  litharge  of  better  quality. 

The  litharge  produced  in  the  English  cupellation  furnace 
is  reduced  to  the  metallic  state  in  a  reverberatory  furnace 
with  a  hearth  measuring  8  feet  by  7,  which  is  lined  with 
bituminous  coal  \  this  soon  becomes  converted  into  a  porous 
coke,  which  protects  the  clay  hearth  of  the  furnace  from 


FIG.  76. — German  Cupellation-furnace. 

being  corroded  by  the  melted  litharge,  and  forms  a  filter 
through  which  the  lead  runs  towards  the  opening  from 
which  it  is  tapped.  About  3  tons  of  litharge  mixed  with 
6  cwts.  of  small  coal  are  charged  at  once  ;  the  carbon  of 
the  coal  removes  the  oxygen  from  the  oxide  of  lead  com 
posing  the  litharge,  and  reduces  the  lead  to  the  metallic 
state.  The  lead  thus  obtained  usually  contains  30  or  40  ozs. 
of  silver  in  a  ton,  and  is  introduced  into  its  appropriate 
place  in  a  series  of  Pattinson's  pans  (p.  194). 


Cupcllation.  213 

The  German  citpellation-furnace  (Figs.  76,  77)  differs  from 
the  English  in  having  a  fixed  instead  of  a  moveablc  hearth 
(A),  covered  with  an  iron  dome  (c)  lined  with  clay,  which  is 
capable  of  being  lifted  off  by  a  crane  (G).  The  hearth  is 
circular,  about  10  feet  wide,  and  is  lined  with  marl,  or  with 
an  intimate  mixture  of  clay  and  lime  well  beaten  and 
hollowed  out  like  a  saucer,  with  a  circular  cavity  about  20 
inches  wide  and  \  inch  deep,  in  the  middle,  for  collecting 
the  cake  of  silver.  Wood  ashes,  previously  washed  and  well 
beaten  down,  are  sometimes  employed  instead  of  marl.  Two 
tuyeres  (a)  direct  the  blast  across  the  hearth,  and  are  pro- 


FIG.  77. — Section  of  German  Cupellation-furnace. 

vided  with  butterfly -valves  for  guiding  the  blast  over  the  sur 
face  of  the  metal.  The  fire-place  (F)  is  situated 'in  a  square 
furnace  adjoining  the  hearth,  and  is  supplied,  when  prac 
ticable,  with  wood,  which  gives  a  longer  and  clearer  flame 
than  coal.  Impure  leads  can  be  treated  by  the  German  pro 
cess,  whilst  the  English  method  of  cupellation  is  adapted  for 
those  which  are  comparatively  free  from  antimony  and  copper. 
From  4  to  17  tons  of  lead  can  be  cupelled  at  once,  accord 
ing  to  the  size  of  the  hearth,  the  pigs  being  placed  upon  a 
thin  layer  of  straw.  The  heat  is  gradually  raised  so  as  to 
melt  the  lead,  no  blast  being  employed  for  the  first  three 
hours.  When  the  metal  is  in  a  state  of  tranquil  fusion,  the 


2 1 4       Metals  :  their  Properties  and  Treatment. 

surface  is  skimmed  to  remove  the  dross,  and  the  bellows  are 
worked  at  the  rate  of  about  four  or  five  strokes  a  minute,  in 
order  to  renew  the  air  over  the  surface,  so  as  to  promote 
oxidation.  In  about  two  hours,  a  stronger  fire  is  applied, 
and  the  crust  of  oxide  and  of  various  mechanical  impurities 
is  skimmed  off  the  surface  through  the  opening  (<?)  provided 
for  the  escape  of  the  litharge.  About  an  hour  and  a  half  is 
occupied  in  thoroughly  cleansing  the  surface  of  the  lead. 

The  blast  is  now  freely  directed  upon  the  melted  metal, 
so  as  to  produce  litharge  abundantly,  and  to  drive  it  in 
waves  through  the  outlet  (o),  which  is  deepened  by  the 
workman  in  proportion  as  the  level  of  the  lead  falls.  The 
litharge  flows  out  on  to  the  floor  of  the  shop  as  at  L.  After 
continuing  the  process  for  a  period  varying  between  seven 
hours  and  sixty  hours  according  to  the  amount  of  lead,  the 
removal  of  the  lead  is  complete  so  far  as  it  can  be  effected 
in  this  furnace,  and  the  phenomena  described  at  p.  211  as 
indicating  the  termination,  are  witnessed.  A  wooden  spout 
is  then  introduced  into  the  charging- door,  through  which 
water  is  carefully  poured  upon  the  surface  of  the  silver  to 
solidify  it  into  a  cake,  which  undergoes  a  subsequent  refining 
to  complete  its  purification. 

The  first  portions  of  oxide  which  form  upon  the  surface 
in  this  process  contain,  beside  the  oxide  of  lead,  oxides  of 
antimony,  iron  and  other  impurities,  and  yield,  when  reduced, 
a  very  impure  lead,  fit  only  for  making  shot  or  type-metal. 
The  last  portions  of  litharge,  amounting  to  about  ^th'of 
the  whole,  are  set  aside  to  be  reduced  separately,  when  they 
furnish  a  lead  rich  in  silver.  When  bismuth  is  present  in 
the  lead,  the  last  portions  of  litharge  have  a  green  colour. 
A  certain  quantity  of  the  intermediate  portion  of  litharge 
(containing  less  than  half  an  ounce  of  silver  in  the  ton)  is 
sent  into  the  market  as  such,  being  useful  to  the  manufac 
turers  of  glass  and  earthenware,  of  sugar  of  lead,  &c.  In 
the  market,  it  finds  a  readier  sale  when  in  reddish  brown 
scales  or  flakes,  which  are  produced  by  running  it  out,  when 


Extraction  of  Silver  at  Mansfeld.  2 1 5 

melted,  into  large  iron  vessels,  and  allowing  it  to  cool  in  a 
draught  of  air.  When  these  vessels  are  inverted,  the  mass 
of  litharge  is  easily  turned  out  and  broken  into  a  flaky 
powder.  Impure  litharge  cannot  be  converted  into  red 
litharge,  so  that  the  colour  is  evidence  of  its  purity. 

The  cupel,  which  is  largely  impregnated  with  litharge  and 
contains  some  silver,  is  broken  up  and  smelted  in  order  to 
extract  those  metals. 

At  Andreasberg  and  Freiberg,  the  silver  ores  are  melted 
with  the  lead  (already  containing  some  silver)  upon  the 
cupel  itself,  when  any  sulphuret  of  silver  which  they  contain 
is  decomposed,  its  sulphur  combining  with  oxygen  to  form 
sulphurous  acid,  and  the  silver  being  dissolved  by  the  lead. 

At  Kongsberg,  the  use  of  a  blast  heated  to  about  400°  F. 
has  been  attended  with  a  great  saving  of  time  and  fuel,  with 
the  additional  advantage  of  cupelling  leads  containing  ten  or 
twelve  parts  of  copper  in  the  hundred,  which  are  too  difficult  to 
fuse  on  the  cold  blast  cupel.  In  a  furnace  six  feet  in  diameter, 
a  charge  of  3^  tons  of  lead  is  cupelled  in  seven  hours. 

The  silver  obtained  by  cupellation  is  liable  to  contain 
small  quantities  of  lead,  bismuth,  antimony,  copper  and 
gold,  the  three  first  of  which  render  it  brittle.  It  is  there 
fore  generally  subjected  to  a  refining  process,  which  consists 
in  exposing  it  in  a  melted  state  to  the  action  of  the.  air,  when 
the  foreign  metals,  with  the  exception  of  the  gold,  are 
oxidised  and  converted  into  a  dross.  The  operation  is 
performed  either  in  an  ordinary  cupellation  furnace,  or  in 
another  constructed  upon  the  same  principle. 

Extraction  of  Silver  from  the  Ores  of  Copper.— The  ores  of 
copper  containing  silver  are  smelted  chiefly  at  Mansfeld,  the 
copper  being  extracted  in  the  form  of  black  copper  by  the 
process  described  at  p.  125.  From  the  black  copper  the 
silver  is  extracted  by  the  process  of  eliquation,  which  consists 
in  alloying  it  with  a  large  proportion  of  lead,  and  afterwards 


2 1 6       Metals :  their  Properties  and  Treatment. 


melting  out  the  latter  metal  by  a  moderate  heat,  when  it 
carries  all  the  silver  with  it,  to  be  afterwards  extracted  by 
cupellation.  The  black  copper  is  broken  into  small  frag 
ments,  or  granulated  by  melting  it  and  running  it  into 

water,  and  is  then  fused  in  a 
small  blast  furnace  with  from 
two  to- four  times  its  weight  of 
lead,  that  which  already  con 
tains  silver  being  chosen  if 
possible,  and  the  two  metals 
thrown  in  alternately.  The 
alloy  of  lead  and  copper  is 
cooled  quickly  in  thick  cast-iron  moulds,  and  chilled  with 
water  in  order  to  avoid  the  separation  of  the  two  metals, 
being  thus  cast  into  round  cakes  18  inches  in  diameter  and 
3  inches  thick.  These  cakes  are  placed  on  a  liquation- 
hearth  (Fig.  78),  which  is  a  gutter  made  by  two  sloping  cast- 
iron  plates  with  a  space  between  them  through  which  the 
lead  trickles  down.  The  cakes  of  copper-lead  (D)  are  set  on 


FIG.  78. — Liquation-hearth. 


FIG.  79. — Liquation-hearth. 

edge  across  this  gutter,  with  pieces  of  wood  to  keep  them 
apart ;  the  gutter  is  then  shut  in  with  iron  plates  (F,  Fig.  79), 
and  filled  with  charcoal.  A  wood  fire  being  made  in  the 
space  (M)  beneath  the  gutter,  the  charcoal  takes  fire  and 
melts  the  lead,  which  runs  into  a  receptacle  (o)  outside  the 


Extraction  of  Silver  by  Amalgamation.        217 


furnace,  carrying  the  silver  with  it.  This  lead  is  cast  into 
ingots  from  which  the  silver  is  extracted  by  cupellation. 
The  liquation  occupies  three  or  four  hours.  The  copper 
cakes  still  retain  about  one-fourth  of  lead  and  some  silver, 
which  are  extracted  by  exposing  them  to  a  higher  tempera 
ture  in  a  sweating-furnace  (Fig.  80)  where  they  are  placed 
over  a  number  of  fire-brick  channels  (F)  in  which  a  wood 
fire  is  made.  The  bulk  of  the  lead  is  converted  into  oxide 
by  the  air  in  the  furnace,  so  that  a  quantity  of  litharge  con 
taining  oxide  of  copper 
and  silver  collects  at  the 
bottom  of  the  channels, 
and  is  fused  with  the 
black  copper  in  the  blast 
furnace  employed  for 
preparing  the  cakes  to 


FIG.  80. — Sweating-furnace.     M,  Back-wall  with 
flues  communicating  with  the  chimney  H. 


be  submitted  to  eliqua- 
tion. 

Extraction  of  Silver 
from  the  Ore  by  Melting 
with  Lead, — At  Kongs- 
berg  in  Norway,  where 
the  ore  contains  its  sil 
ver  in  the  metallic  state, 
it  is  extracted  by  simply  melting  the  dressed  ore  with  its  own 
weight  of  lead,  when  an  .alloy  containing  about  one-third  of 
its  weight  of  silver  is  obtained,  which  is  submitted  to  the 
process  of  cupellation.  When  ores  containing  sulphuret  of 
silver  are  melted  with  lead,  this  metal  removes  the  sulphur 
in  the  form  of  sulphuret  of  lead,  and  the  liberated  silver  is 
dissolved  by  another  portion  of  lead. 

AMALGAMATION    PROCESS     FOR    THE    EXTRACTION    OF   SILVER 
FROM    ITS    ORES. 

The  process  of  amalgamation  is  so  called  because  the 
silver  is  extracted  in  the  form  of  an  amalgam  with  mercury, 


2 1 8       Metals :  their  Properties  and  Treatment. 

and  there  are  two  modes  of  carrying  it  out,  the  choice  being 
regulated  by  the  scarcity  or  abundance  of  fuel  in  the 
locality.  Thus,  the  amalgamation  process  employed  in 
Mexico  and  Chili,  where  fuel  is  dear,  is  very  different  from 
that  in  use  in  Freiberg  where  it  may  be  had  in  abundance. 

Mexican  Process  of  Amalgamation. — In  Mexico  and  Chili, 
where  the  silver  ores  obtained  from  the  western  slopes  of 
the  Cordilleras  are  treated,  the  thorough  pounding  of  the 
ores  and  of  the  materials  added  to  them,  by  the  compara 
tively  inexpensive  agency  of  water-power,  horses  and  mules, 
is  employed  to  facilitate  the  chemical  changes  which  would 
be  promoted  by  the  action  of  fire,  if  fuel  were  more  abundant. 
Time  is  also  an  important  element  in  this  process,  which 
consists  essentially  in  converting  the  whole  of  the  silver  into 
chloride  of  silver,  to  be  afterwards  brought  to  the  metallic 
state  by  the  action  of  mercury,  and  dissolved  by  the  latter, 
in  the  form  of  an  amalgam. 

The  ore  sometimes  contains  only  35  ozs.  of  silver  in  the 
ton,  partly  in  the  metallic  state,  and  partly  as  chloride  and 
sulphuret  of  silver,  and  is  carefully  picked  over  in  order 
that  the  worthless  portions  may  be  rejected.  It  is  then 
crushed  in  oblong  mortars  under  wooden  pestles,  shod  with 
iron,  weighing  about  200  Ibs.  each,  and  raised  by  cams  pro 
jecting  from  an  axle  moved  by  a  water-wheel.  The  crushed 
ore  is  ground  with  water  into  a  mud,  under  granite  stones, 
which  are  made  to  revolve  in  a  granite  bed  by  the  labour  of 
mules.  This  mud  is  transferred  to  the  amalgamation-floor, 
an  enclosure,  about  300  feet  by  240  feet,  paved  with  stone. 
It  is  there  mixed,  with  wooden  shovels,  with  a  proportion  of 
common  salt,  varying  from  one  to  five  parts  for  every  hun 
dred  parts  of  ore,  and,  in  order  to  effect  a  thorough  inter 
mixture,  a  number  of  horses  are  made  to  .trample  the  mud 
in  the  enclosure,  after  which  it  is  left  at  rest  for  some  hours. 

On  the  following  morning,  the  horses  are  again  turned 
into  the  amalgamation-floor  for  an  hour,  after  which,  copper 
pyrites  which  has  been  roasted  and  ground  to  powder  (when 


Mexican  Amalgamation  Process.  219 

it  is  called  magistral]  is  added  in  the  proportion  of  3^th  or 
Toijth  of  the  weight  of  the  ore.  Six  horses  attached  to  a 
halter  held  by  a  man  in  the  centre,  are  then  made  to  tram 
ple  the  mud  for  five  or  six  hours. 

The  magistral  contains  about  TVth  of  its  weight  of  sulphate 
of  copper,  which  decomposes  the  common  salt  (chloride  of 
sodium),  yielding  sulphate  of  sodium  and  chloride  of  copper. 

The  mixture  is  now  ready  for  the  amalgamation  with 
mercury,  which  is  sprinkled  upon  it  from  a  bag  of  coarse 
canvas,  in  quantity  about  twice  that  of  the  silver  present  in 
the  ore.  It  is  then  trodden  again  by  horses',  and  well  turned 
with  wooden  shovels,  these  operations  being  repeated  every 
other  day  until,  on  washing  a  small  sample  in  a  bowl,  it  is 
found  that  all  the  mercury  which  has  been  added  is  in  com 
bination  with  the  silver,  as  an  amalgam,  no  globules  of  mer 
cury  being  visible. 

The  chloride  of  silver  has  been  decomposed  by  the  mer 
cury,  forming  chloride  of  mercury  (calomel}  and  metallic 
silver,  the  latter  having  combined  with  the  mercury  to  form 
an  amalgam  of  silver. 

The  chloride  of  copper  is  also  decomposed  by  the  mer 
cury,  which  abstracts  half  its  chlorine,  forming  calomel,  and 
leaves  the  subchloride  of  copper,  which  is  dissolved  by  the 
solution  of  common  salt,  and  being  thus  exposed  to  the 
action  of  air,  absorbs  oxygen  to  form  an  oxychloride  of  copper; 
the  latter  acts  upon  the  sulphuret  of  silver,  its  oxygen  con 
verting  the  sulphur  into  sulphuric  acid,  whilst  the  silver  is 
set  free,  to  be  dissolved  by  the  mercury.  The  subchloride 
of  copper,  having  thus  been  reproduced,  is  ready  to  absorb 
more  oxygen  from  the  air,  and  to  act  upon  a  fresh  quantity 
of  the  sulphuret  of  silver. 

The  older  theory,  which  has  not  been  found  to  accord 
with  practice,  regarded  the  sulphuret  of  silver  as  being  de 
composed  by  the  subchloride  of  copper,  with  formation  of 
sulphuret  of  copper  and  chloride  of  silver,  the  latter  being 
afterwards  decomposed  by  the  mercury,  as  stated  above. 


22O       Metals :  their  Properties  and  Treatment. 

This  examination  of  the  amalgam  also  shows  whether  too 
much  sulphate  of  copper  (in  the  form  of  magistral)  has  been 
added.  If  this  be  the  case,  a  quantity  of  the  mercury  will 
be  found  to  be  so  finely  divided  as  to  form  a  dark-coloured 
mud,  and  occasional  brown  spots  of  metallic  copper  will  be 
visible.  A  great  loss  of  mercury  would  ensue  if  the  magistral 
had  been  added  in  excess,  because  the  chloride  of  copper 
formed  from  it  would  be  decomposed  by  the  mercury,  yield 
ing  a  chloride  of  mercury  (calomel)  and  subchloride  of 
copper. 

If  it  is  found  that  this  error  has  been  committed,  a  little 
lime  is  added  to  the  contents  of  the  amalgamation-floor 
to  decompose  the  chloride  of  copper  (forming  chloride  of 
calcium  and  oxide  of  copper)  and  prevent  any  further  waste 
of  mercury. 

It  sometimes  occurs,  on  washing  the  sample,  that  globules 
of  mercury  are  perceived,  showing  that  it  has  not  entirely 
united  with  the  silver.  This  is  due  to  an  insufficient  supply 
of  magistral,  in  consequence  of  which  the  amount  of  chloride 
of  copper  formed  has  not  been  sufficient  to  convert  the  whole 
of  the  silver  into  chloride  of  silver,  a  form  in  which  it  is 
much  more  readily  acted  upon  by  the  mercury  than  when  it 
is  in  the  state  of  sulphuret  of  silver,  because  the  chloride  of 
silver  is  capable  of  being  dissolved  by  the  strong  solution  of 
common  salt  existing  in  the  mud,  and  is  thus  presented  to 
the  mercury  in  the  condition  most  favourable  to  chemical 
action.  If  necessary,  a  further  addition  of  the  roasted  cop 
per  pyrites  is  made  before  proceeding  with  the  amalgamation. 

After  about  a  fortnight,  a  fresh  quantity  of  mercury  is 
added,  rather  less  than  one-third  of  the  first  addition,  and 
the  operation  of  trampling  is  repeated.  When  this  mercury 
has  also  been  taken  up,  a  third  portion,  about  half  as  large 
again  as  the  second,  is  added,  in  order  to  dissolve  the 
amalgam  of  silver  in  an  excess  of  mercury.  After  a  thorough 
incorporation  by  trampling,  the  mixture  is  at  once  shovelled 
into  barrows  and  taken  to  the  washing-vat,  which  is  a  circular 


Mexican  Amalgamation  Process.  221 

cistern  8  feet  wide  and  9  feet  deep,  in  which  the  mud  from 
the  amalgamating-floor  is  well  stirred  up  with  water,  by  an 
agitator  worked  by  four  mules,  fresh  water  constantly  running 
into  the  cistern,  and  carrying  off  the  earthy  matter  over  the 
side. 

The  liquid  amalgam  left  behind  is  thrown  into  a  leather 
bag  with  a  canvas  bottom,  through  which  the  excess  of 
mercury  is  strained  off,  leaving  a  pasty  amalgam  containing 
about  |th  or  ^th  of  its  weight  of  silver,  which  is  subjected  to 
pressure  in  order  to  squeeze  out  more  mercury  and  convert 
it  into  a  hard  solid  mass.  This  is  moulded  into  wedge- 
shaped  masses  of  about  30  Ibs.  each,  which  are  built  up  into 
a  circular  tower  on  a  copper  stand  having  a  hole  in  its 
centre  through  which  a  pipe  passes  in  order  to  conduct  the 
mercurial  vapours  into  a  tank  of  water  placed  beneath. 
The  pile  of  amalgam  is  covered  with  an  iron  bell,  the  opening 
of  which  fits  tightly  upon  the  copper  stand,  any  crevices 
being  carefully  filled  up  with  a  cement.  A  temporary  fur 
nace  is  built  with  bricks  around  the  bell,  and  kept  full  of 
burning  charcoal  for  about  twenty  hours,  when  all  the 
mercury  is  converted  into  vapour,  which  condenses  in  the 
water  beneath,  and  the  silver  is  left  as  a  hard  mass  ;  this  is 
broken  up,  melted,  and  cast  into  bars  weighing  about  1000 
ozs.  each. 

The  period  occupied  by  the  amalgamation  process  varies 
greatly  according  to  the  nature  of  the  ores,  extending  some 
times  over  little  more  than  a  fortnight,  and  sometimes 
requiring  six  or  eight  weeks. 

The  loss  of  mercury  in  the  process  is  very  considerable, 
amounting  to  about  24  ozs.  for  every  pound  of  silver  obtained, 
being  due,  in  great  part,  to  the  flouring  or  fine  division  of 
the  metal,  which  is  then  carried  away  in  the  process  of 
washing,  together  with  all  the  silver  which  has  been  dis 
solved  in  it. 

The  hot  amalgamation,  applied  for  extracting  the  silver 
from  rich  ores  which  contain  it  either  in  the  metallic  state 


222       Metals :  their  Properties  and  Treatment. 

or  as  chloride,  bromide  or  iodide,  only  occupies  five  or  six 
hours,  and  entails  less  loss  of  mercury.  It  consists  in  boiling 
the  finely-powdered  ore  with  water,  common  salt  (10  or  15 
parts  for  a  hundred  of  ore)  and  mercury,  in  pans  with 
copper  bottoms,  when  the  chloride,  bromide  and  iodide  of 
silver  are  decomposed  by  the  copper,  forming  a  chloride, 
bromide  or  iodide  of  copper,  and  liberating  the  silver,  which 
is  dissolved  by  the  mercury. 

The  extraction  of  silver  (and  of  gold)  by  amalgamation 
is  very  much  facilitated  by  adding  a  minute  proportion  of 
sodium  to  the  mercury  employed,  for  it  is  found  that  mercury 
so  treated  attacks  and  dissolves  silver  and  gold  much  more 
readily  than  pure  mercury,  and  that  it  is  very  much  less 
liable  to  assume  that  finely  divided  state  in  which  it  is  so 
readily  washed  away  and  lost. 

Since  sodium  is  rapidly  oxidised  by  exposure  to  air,  and 
decomposes  water  with  explosive  violence,  it  is  not  a  very 
portable  substance ;  hence  it  is  better  that  it  should  be 
carried  in  the  form  of  a  strong  amalgam  of  sodium  which 
may  be  diluted  with  the  proper  quantity  of  mercury  on  the 
spot  where  it  is  to  be  used. 

The  strong  amalgam  is  prepared  by  heating  too  parts  of 
mercury  to  about  300°  F.,  in  an  iron  vessel  with  a  narrow 
neck,  and  adding,  in  small  pieces  (since  the  combination  is 
very  violent),  15  parts  of  metallic  sodium;  the  amalgam  is 
then  poured  out  into  ingot  moulds,  where  it  solidifies  into 
very  brittle  crystalline  bars.  One  part  of  this  amalgam  is 
melted  by  a  gentle  heat  and  mixed  with  about  five  thousand 
parts  of  mercury  before  employing  it  in  the  amalgamating 
process.  The  action  of  the  sodium  appears  to  depend  upon 
its  highly  electropositive  character,  but  its  mode  of  operation 
does  not  appear  to  be  as  yet  well  understood. 

Amalgamation  Process  for  Extraction  of  Silver  at  Freiberg. 
—The  process  adopted  for  extracting  the  silver  from  the 
ores  mined  in  Saxony  is  far  less  wasteful  of  mercury  than  the 
Mexican  process  just  described,  the  loss  varying  from  4  to 


Amalgamation  at  Freiberg.  223 

12  ozs.  per  Ib.  of  silver,  since  this  valuable  metal  is  employed 
only  for  the  purpose  of  dissolving  the  silver  after  it  has  been 
brought  into  the  metallic  state,  whereas  in  Mexico,  a  part  of 
the  mercury  is  used  in  removing  the  chlorine  from  the 
chloride  of  silver  in  order  to  liberate  the  metal.  In  the 
Saxon  process,  as  in  the  Mexican,  the  whole  of  the  silver  is 
converted  into  chloride  of  silver,  from  which  the  chlorine  is 
removed  by  the  action  of  metallic  iron,  and  the  silver,  which 
has  thus  been  reduced  to  the  metallic  state,  is  dissolved  by 
mercury. 

The  ore  treated  at  Freiberg  contains  the  silver  chiefly  as 
a  sulphuret,  but  it  also  contains  the  sulphurets  of  several 
other  metals,  particularly  of  antimony,  bismuth,  arsenic,  iron, 
copper,  lead  and  zinc.  The  different  kinds  of  ore  are 
sorted  and  mixed  so  that  the  mixture  may  contain  less  than 
one  part  of  copper  and  five  parts  of  lead  in  the  hundred 
parts,  for  both  these  are  easily  taken  up  by  the  mercury, 
causing  undue  consumption  of  that  metal.  The  silver 
present  in  the  mixed  ores  should  amount  to  about  80  ozs. 
in  the  ton.  The  presence  of  a  large  proportion  of  iron 
pyrites  (bisulphuret  of  iron)  is  necessary  for  the  subsequent 
chemical  changes,  so  that  the  mixture  is  made  to  contain 
about  one-third  of  its  weight  of  that  mineral. 

The  ore  thus  prepared  is  ground  to  a  coarse  powder, 
mixed  with  one-tenth  of  its  weight  of  common  salt,  and 
roasted  upon  the  hearth  of  a  reverberatory  furnace  at  a  dull 
red  heat,  for  about  two  hours,  care  being  taken  to  turn  it 
over  frequently,  and  to  avoid  fusion.  During  the  roasting, 
th£  oxygen  of  the  air  converts  the  arsenic  and  antimony  into 
their  respective  oxides,  which  pass  off  as  a  thick  white 
smoke,  together  with  some  sulphurous  acid  produced  by  the 
combustion  of  the  sulphur.  The  sulphurets  of  copper,  iron 
and  silver,  also  combine  with  oxygen,  and  become  converted 
into  the  sulphates  of  those  three  metals. 

The  temperature>is  then  raised  to  enable  the  sulphates  of 
copper,  iron  and  silver  to  decompose  the  chloride  of  sodium 


224       Metals:  their  Properties  and  Treatment. 


FIG.  81. — Amalgamation  Cask,  a, 
Opening  for  charging,  and  dis 
charging,  rr",  Toothed  wheel 
for  receiving  n 
axis  (Fig.  82). 


(common  salt)  yielding  sulphate  of  sodium,  and  chlorides  of 
copper,  iron  and  silver.  Other  chemical  changes  also  occur 
in  this  stage,  but  it  will  not  be  necessary  to  trace  them, 

since  they  do  not  affect  the  ex 
traction  of  the  silver. 

The  first  roasting  is  effected 
with  a  coal  fire,  and  the  second 
heating  with  fir-wood. 

The  deep  brown  roasted  ore, 
containing  the  sulphate  of  silver, 
is  now  sifted,  and  the  lumps 
mixed  with  more  salt,  and  roasted 
again  in  order  to  complete  the 
change. 

The  sifted  powder  is  ground 
to  a  very  fine  meal,  and  intro- 
from  the  duced  in  charges  of  half  a  ton 
into  strong  oaken  casks  (Fig.  81), 
about  three  feet  each  way,  containing  three  hundred  weights 
of  water,  and  mounted,  to  the  number  of  twenty,  on  cast-iron 

axles,  so  that  they  can 
be  made  to  revolve  at 
.  pleasure  by  being  con 
nected  with  the  axle 
(A,  Fig.  82)  of  a  water- 
wheel.  About  one  hun 
dred  weight  of  wrought 
iron,  in  fragments,  is 
put  into  each  of  the 
casks,  which  are  then 
made  to  revolve  at  the 
rate  of  ten  or  twelve 
turns  in  a  minute.  The 
iron  removes  the  chlorine  from  the  chloride  of  silver,  pro 
ducing  chloride  of  iron  and  metallic  silver,  which  remains 
dispersed  through  the  mixture  in  a  finely-divided  condition. 


FIG.  82. — Amalgamation  of  Silver  Ores  at  Frei 
berg.  rr'1,  Toothed  wheels  for  transmitting 
motion  from  the  axis  A  B.  m  m' ,  Troughs  for 
receiving  the  contents  of  the  casks  C. 


Amalgamation  at  Freiberg.  225 

The  iron  also  decomposes  the  chloride  of  copper  in  a  similar 
manner,  yielding  finely  divided  metallic  copper. 

After  having  revolved  for  about  two  hours,  the  casks  are 
opened  for  the  purpose  of  introducing  the  mercury  to  dis 
solve  the  silver ;  but  before  adding  this,  the  contents  must 
be  brought  to  a  proper  consistence  ;  if  they  are  too  thick, 
they  could  not  be  well  mixed  with  the  mercury,  and  some 
more  water  must  be  added  ;  on  the  other  hand,  if  they  are 
very  liquid,  the  mercury  will  at  once  go  to  the  bottom,  and 
will  never  be  thoroughly  distributed  through  the  mixture ; 
some  more  of  the  prepared  ore  must  then  be  introduced. 
5  cwts.  of  mercury  are  then  poured  into  each  of  the  casks,  and 
they  are  made  to  revolve,  at  the  rate  of  about  twenty-five  turns 
in  a  minute,  for  sixteen  or  eighteen  hours,  when  the  mercury 
dissolves  the  metallic  silver  and  copper.  During  this  process, 
the  contents  of  the  casks  are  twice  examined  in  order  to  see 
if  they  have  a  proper  consistence.  The  chemical  action 
which  takes  place  in  the  casks  raises  their  temperature,  even 
in  winter,  to  about  100°  F. 

In  a  more  modern  arrangement,  the  casks  are  fixed  in  a 
vertical  position,  the  materials  being  mixed  by  a  revolving 
agitator  with  iron  arms.  Steam  is  admitted  into  the  casks 
through  holes  at  the  bottom,  in  order  to  facilitate  the  amal 
gamation  by  its  heat. 

When  this  rotation  is  finished,  the  amalgam  of  silver  and 
copper  is  found  interspersed  in  minute  globules  throughout 
the  mass  ;  in  order  to  collect  it,  the  casks  are  filled  with  water, 
and  revolved  eight  times  in  a  minute,  during  about  two  hours. 
They  are  then  turned  with  their  wooden  bungs  «  Fig.  83) 
downwards,  and  the  pegs  stopping  the  small  openings  in  the 
bungs  being  withdrawn,  a  tube  with  a  stopcock  is  inserted  ; 
so  that  the  amalgam  may  run  out  into  a  trough  beneath. 
The  mixture  in  the  casks  is  emptied  out  through  a  grating 
which  retains  the  pieces  of  iron,  whilst  the  mud  is  collected 
in  tubs,  where  it  is  stirred  with  water  and  allowed  to  deposit 
the  small  quantity  of  amalgam  which  has  been  carried  away. 

.Q 


226      Metals:  tJicir  Properties  and  Treatment. 

The  mud  is  afterwards  allowed  to  settle  down  so  that  it 
may  be  again  treated  by  the  amalgamation  process,  when  it 
yields  about  4-^  ounces  of  silver  for  a  ton. 

The  liquid  amalgam  of  silver  and  copper  is  strained 
through  canvas  bags,  as  in  the  Mexican  process,  when  a 
quantity  of  liquid  mercury  runs  off  (containing  about  20  ozs. 
of  silver  to  the  ton),  leaving  in  the  bags  a  pasty  amalgam 
containing  about  30  parts  of  mercury,  4  parts  of  silver,  and 


FIG.  83. — Amalgamation  of  Silver  Ores  at  Freiberg.  E,  Reservoirs  for  the 
ground  mineral.  /,  Leathern  pipe  for  conveying  it  into  the  opening  a  of 
the  cask  c.  n,  Cisterns  containing  water.  ;/;  u  in1,  Receptacles  for  the 
amalgam  and  spent  charge,  i  i',  Pipe  for  conveying  the  amalgam  into 
the  gutter  h. 

i  part  of  copper,  with  small  quantities  of  other  metals  which 
existed  in  the  ore,  particularly  lead,  bismuth,  zinc,  antimony, 
and  gold.  The  amalgam  is  sometimes  allowed  to  settle  in 
a  narrow  wooden  cylinder,  8  feet  high,  before  being  strained 
in  the  bags,  when  it  separates  into  two  layers,  the  lower  con 
sisting  chiefly  of  mercury,  which  need  not  be  strained. 
The  pressure  is  sometimes  applied  to  the  amalgam  by  a 


Distillation  of  Silver  A  malgam. 


227 


screw,  and  sometimes  by  the  hydraulic  press ;  in  the  latter 
case  the  amalgam  is  placed  in  an  iron  cylinder  with  a  wooden 
bottom  through  which  the  liquid 
mercury  is  pressed  out. 

This  pasty  amalgam  is  made  up 
into  balls  which  are  placed  in  iron 
dishes  (Fig.  84)  supported  at  about 
five  inches  apart  by  an  iron  rod 
which  runs  through  their  centres, 
and  stands,  upon  four  feet,  in  an 
iron  basin  of  water.  When  about 
3cwts.  of  amalgam  have  been  placed 
in  the  dishes,  an  iron  bell  is  let 
down  over  them,  by  a  crane,  its 
lower  opening  resting  in  the  water. 
A  fire  is  then  made  around  the  up 
per  part  of  the  bell,  first  with  wood,  then  with  turf,  and  finally 
with  charcoal.  In  this  way  the  bell  is  made  red  hot,  and 
the  mercury  is  converted  into  vapour,  condensing  in  the 
water  beneath,  which  is  kept  constantly  cool  by  the  passage 
of  cold  water  through  a  wooden  trough  in  which  the  iron 


nfflwi-ts 


FIG.  84. — Distillation  ot  the 
Amalgam  of  Silver. 


FIG.  85. — Apparatus  for  distillation  of  the  Amalgam  of  Silver. 

basin  stands.  After  about  eight  hours,  no  more  globules  oi 
mercury  are  heard  to  drop  into  the  water,  and  the  distilla 
tion  is  finished.  On  removing  the  bell,  spongy  masses  of 

Q  2 


228       Metals:  tlieir  Properties  and  Treatment. 

the   alloy   of  silver,    copper,    &c.,    are   found   in    the  iron 
dishes. 

A  more  modern  and  economical  apparatus  for  the  distil 
lation  of  the  pasty  amalgam  consists  of  an  iron  crucible  (£, 
Fig.  85)  22  inches  wide  and  n  inches  deep,  which  is  heated 
by  a  charcoal  fire(^),  the  vapour  of  mercury  being  conducted 
by  an  iron  hood  (c)  into  an  iron  condensing  tube  (g)  which 
traverses  a  cistern  of  water  (<?).  The  inside  of  the  crucible  is 
coated  with  lime,  and  an  iron  plate  coated  with  lime  is  fitted 
into  the  crucible,  which  is  withdrawn  with  the  silver  adhering 
to  it  at  the  close  of  the  operation.  4  cwts.  of  amalgam  are 
distilled  in  five  hours. 

The  alloy  left  after  distilling  the  amalgam  is  melted  in 
crucibles  made  of  a  mixture  of  fire-clay  and  plumbago,  and 
briskly  stirred  with  an  iron  rod.  Fumes  of  the  oxides  of 
bismuth,  zinc  and  antimony  are  given  off,  and  a  scum  con 
taining  oxides  of  lead  and  copper  forms  upon  the  surface, 
and  is  skimmed  off.  When  no  more  dross  appears  upon  the 
surface,  the  metal  is  cast  into  ingots.  It  still  contains  about 
one-seventh  of  its  weight  of  copper,  from  which  it  is  purified 
by  melting  it  with  lead,  and  subjecting  it  to  cupellation 
(p.  208),  when  the  litharge  dissolves  the  copper  in  the  form 
of  oxide,  and  the  silver  is  left  pure. 

Treatment  of  Copper-matt s  for  Silver.  —  When  the  last 
matts  (corresponding  to  the  Welsh  fine  metal)  obtained  in 
the  copper-smelting  at  Mansfeld  (p.  125)  contain  any  con 
siderable  proportion  of  silver  (not  less  than  2-J-  parts  in  a 
thousand),  it  is  extracted  by  a  process  closely  resembling 
that  employed  at  Freiberg.  Since,  however,  these  matts 
consist  almost  entirely  of  sulphuret  of  copper  and  sulphuret 
of  iron,  so  large  a  quantity  of  the  sulphates  of  these  metals 
is  formed  during  the  roasting,  that  it  is  found  necessary  to 
mix  the  roasted  ore  with  a  quantity  of  chalk  equal  to  that  of 
the  common  salt ;  when  the  lime  in  the  chalk  decomposes 
the  sulphates  of  iron  and  copper,  forming  sulphate  of  lime, 
and  leaving  the  iron  and  copper  in  the  form  of  oxides. 


Angus  tin's  Process  for  extracting  Silver. 

The  mud  emptied  from  the  tubs  at  the  close  of  the 
amalgamation  process,  at  Mansfeld,  is  mixed  with  clay,  and 
made  up  into  cakes,  which  are  dried  and  smelted  in  a  small 
blast-furnace  to  obtain  the  copper. 

Processes  employed  to  supersede  the  Amalgamation  of  Silver 
Ores.  (Aiigustirfs  Pram.)— Several  methods  have  been 
proposed  from  time  to  time  to  avoid  the  use  of  mercury  in 
extracting  silver  from  its  ores.  For  example,  after  roasting 
the  ores,  first  by  themselves,  and  afterwards  in  admixture 
with  common  salt,  as  in  the  Freiberg  process,  to  convert  the 
whole  of  the  silver  into  chloride,  the  latter  is  dissolved  out 
with  a  saturated  solution  of  common  salt,  and  the  chloride 
of  silver  in  the  solution  is  decomposed  by  leaving  it  in  con 
tact  with  scraps  of  copper,  when  the  latter  combines  with 
the  chlorine,  forming  a  chloride  of  copper,  and  the  silver  is 
separated  in  the  finely-divided  metallic  state,  to  be  after 
wards  melted  and  cast  into  ingots.  It  has  been  recom 
mended  to  mix  chlorine-water  with  the  solution  of  common 
salt  employed  in  this  process,  in  order  to  extract  the  gold  at 
the  same  time. 

This  process  has  been  employed  with  satisfactory  results, 
at  Freiberg,  for  the  extraction  of  silver  from  the  matt  con 
taining  two-thirds  of  its  weight  of  copper  obtained  in  the 
copper-smelting  process.  The  matt,  having  been  roasted  by 
itself,  and  afterwards  with  common  salt,  is  stamped  to 
powder,  sifted,  and  placed,  in  quantities  of  about  6  cwts.,  iu 
tubs  with  perforated  bottoms,  over  which  a  linen  strainer  is 
stretched.  A  hot  strong  solution  of  salt  being  let  in  from  a 
reservoir,  dissolves  the  chloride  of  silver  and  carries  it 
through  the  strainer  into  tubs  also  provided  with  a  strainer, 
and  containing  some  spongy  copper  (cement  copper,  see 
p.  128),  which  is  gradually  dissolved,  as  chloride  of  copper, 
whilst  metallic  silver  is  deposited  in  its  stead ;  this  is  removed 
from  the  tubs,  washed  with  muriatic  acid  to  remove  particles 
of  copper,  then  with  water,  and  moulded  into  small  balls, 
which  are  dried  and  fused. 


230      Metals :  their  Properties  and  Treatment. 

The  liquid  containing  the  chloride  of  copper  and  common 
salt  is  conveyed  into  another  series  of  tubs  containing 
copper,  in  order  to  ensure  the  complete  removal  of  the 
silver,  and  afterwards  into  vessels  containing  iron,  which 
causes  the  separation  of  the  metallic  copper,  to  be  used  over 
again  for  precipitating  the  silver. 

The  matt,  having  been  washed  with  solution  of  salt,  until  a 
copperplate  dipped  into  the  liquor  is  no  longer  whitened  by 
the  deposition  of  silver,  is  washed  with  water,  and  taken  to 
the  copper-smelting  furnace  (p.  125). 

Patera's  process,  as  carried  out  at  Joachimstal,  is  appli 
cable  only  to  rich  ores,  and  consists  in  roasting  with  common 
salt,  as  at  Freiberg,  in  order  to  convert  the  silver  into 
chloride  of  silver,  which  is  then  dissolved  out  by  a  cold 
dilute  solution  of  hyposulphite  of  soda,  which  takes  up 
chloride  of  silver  much  more  readily  than  common  salt 
does.  The  solution  is  then  mixed  with  a  solution  of 
sulphuret  of  sodium,  which  produces  a  black  precipitate  of 
stilphuret  of  silver,  and  leaves  the  solution  of  hyposulphite 
ready  to  be  employed  for  treating  a  fresh  portion  of  ore. 
The  sulphuret  of  silver  is  collected  on  a  canvas  strainer, 
washed,  dried,  roasted  to  burn  off  part  of  the  sulphur,  and 
melted  in  black  lead  crucibles  with  metallic  iron,  which 
takes  up  the  rest  of  the  sulphur,  in  the  form  of  sulphuret  of 
iron,  and  leaves  metallic  silver.  The  sulphuret  of  iron  dis 
solves  a  part  of  the  silver,  and  is  worked  up  with  a  fresh 
charge  of  ore. 

ZiervogePs  Process. — A  still  simpler  process  consists  in 
roasting  the  ore  or  matt  containing  the  sulphurets  of  copper, 
iron  and  silver,  so  that  these  may  combine  with  oxygen 
from  the  air,  and  become  converted  into  sulphates,  which  are 
then  heated  so  strongly  as  to  decompose  the  sulphates  of 
copper  and  iron,  leaving  these  metals  as  insoluble  oxides, 
whilst  the  sulphate  of  silver  is  left  undecomposed,  and  may 
be  dissolved  out  by  water  and  placed  in  contact  with 
metallic  copper,  which  separates  the  silver  in  the  metallic 


Ziervogtf  s  Process  for  extracting  Silver.       231 

state,  and  takes  its  place  in  the  solution,  yielding  sulphate 
of  copper. 

Ziervogel's  process  has  been  attended  with  very  satisfac 
tory  results  in  its  application  to  the  extraction  of  silver  from 
the  copper-matts  at  Mansfeld,  containing,  in  100  parts,  80 
parts  of  subsulphuret  of  copper,  n  parts  of  sulphuret  of 
iron,  and  -fths  part  of  sulphuret  of  silver.  The  loss  of  silver 
experienced  in  treating  this  matt  by  the  amalgamation  pro 
cess  amounted  to  nearly  ^th  of  the  metal  present,  by 
Augustin's  process  to  nearly  -jVth.  and  by  Ziervogel's  process 
to  only  T^th. 

The  matt,  having  been  granulated,  ground,  and  sifted,  is 
roasted  with  great  care  and  judgment,  in  reverberatory  fur 
naces,  seven  of  which  are  connected  with  a  single  chimney 
154  feet  high.  The  roasting  occupies  about  ten  hours,  and 
is  continued  until  a  small  sample  taken  out  and  mixed  with 
water  gives  a  liquor  which  produces  a  strong  precipitate  of 
chloride  of  silver  on  the  addition  of  common  salt  (chloride 
of  sodium),  and  has  a  light  blue  colour,  from  a  little  sulphate 
of  copper  having  been  left  undecomposed. 

The  roasted  muss  is  then  introduced,  in  quantities  of 
5  cwts.,  into  tubs  similar  to  those  used  in  Augustin's  process 
(p.  229),  and  treated  with  hot  water  containing  a  little 
sulphuric  acid,  until  the  liquor  which  runs  off  no  longer 
becomes  milky  when  mixed  with  common  salt,  showing  it  to 
be  free  from  silver.  The  solution  of  sulphate  of  silver,  thus 
obtained,  is  run  into  tubs  containing  copper,  where  the  silver 
is  precipitated,  and  is  afterwards  washed  with  diluted  sul 
phuric  acid  to  remove  adhering  copper. 

The  sulphate  of  copper  in  solution  is  decomposed  by 
metallic  iron,  and  the  copper  is  employed  for  precipitating 
the  silver. 

The  copper  matt  of  Freiberg  is  sometimes  roasted,  to 
convert  the  sulphuret  of  copper  into  oxide,  and  is  then 
boiled  in  leaden  tubs  with  diluted  sulphuric  acid,  which 


232       Metals :  tlicir  Properties  and  Treatment. 

dissohes  the  oxide  of  copper  in  the  form  of  sulphate  of 
copper ;  this  salt  is  obtained  in  marketable  crystals  from  the 
solution.  The  residue,  which  contains  the  silver  and  gold, 
is  washed,  mixed  with  half  its  weight  of  litharge,  and  made 
up  into  balls,  which  are  dried  and  smelted  together  with 
more  litharge  and  lead-slags,  when  the  lead  obtained  con 
tains  all  the  silver  and  gold,  which,  are  recovered  from  it  by 
cupellation. 

Very  poor  ores  have  sometimes  been  treated  by  melting 
them,  either  in  cupola  or  reverberatory  furnaces,  with  iron 
pyrites,  which  takes  up  the  silver.  By  smelting  this  pyrites 
together  with  galena,  the  silver  is  obtained  with  the  lead, 
which  may  be  separated  from  it  as  usual  (p.  194). 

A  considerable  quantity  of  silver  is  now  extracted  from 
the  Wicklow  pyrites  (sold  as  silver  smalls),  after  it  has  been 
calcined  for  its  sulphur,  in  the  manufacture  of  sulphuric 
acid. 

Applicatiojis  of  Silver. — Pure  silver  is  far  too  soft  to  resist 
the  wear  to  which  it  is  subjected  in  common  use.  It  is 
therefore  hardened  by  alloying  it  with  copper,  a  consider 
able  quantity  of  which  may  be  added  without  material  altera 
tion  of  colour.  The  hardest  alloy  is  that  which  contains  4 
parts  of  silver  and  i  part  of  copper.  The  standard  silver 
used  for  coin  and  for  silver  articles  in  England  contains,  in 
100  parts,  92^  parts  of  silver  and  7^  parts  of  copper ;  the 
French  silver  coinage  contains  90  parts  of  silver  and  10  parts 
of  copper.  When  the  copper  exceeds  this  amount,  it  is 
oxidised  when  the  alloy  is  exposed  to  the  air,  whence  the 
tarnished  appearance  of  the  silver  coinage  of  Prussia,  which 
contains  one-fourth  of  copper. 

In  English  commerce,  the  purity  or  fineness  of  silver  is 
generally  expressed  as  so  many  pennyweights  (dvvts.)  better 
or  worse  than  the  standard  silver,  of  which  the  troy  pound 
contains  n  ozs.  2  dwts.  of  pure  silver  and  iSdwts.  of  copper 
(commonly  called  alloy].  Thus  the  French  coin,  which 
contains  24  dwts.  of  copper  in  the  troy  pound,  would  be 


Frosted  and  Oxidised  Silver.  233 

described  as  worse  6  dwts.,  because  it  contains  that  quantity 
less  silver  than  the  English  coin.  Mexican  dollars  contain 
23^  dwts.  of  copper  in  the  troy  pound,  being  worse  5^  du>ts. 
Indian  rupees  sometimes  contain  only  12  dwts.  of  copper  in 
the  troy  pound ;  hence  they  are  better  6  dwts.,  that  is,  they 
contain  6  dwts.  more  silver  than  the  English  standard. 

The  specific  gravity  of  English  silver  coin  is  10-3,  and 
since  all  the  alloys  used  to  make  counterfeits  have  tin  for 
their  chief  constituent,  they  have  usually  a  lower  specific 
gravity,  so  that  the  best  method  by  which  to  test  whether  a 
florin,  for  example,  is  good,  without  injuring  it,  is  to  ascer 
tain  its  specific  gravity,  by  weighing  it  first  in  the  ordinary 
way,  and  afterwards  when  suspended  in  water,  and  dividing 
its  weight  in  air  by  the  loss  of  weight  in  water,  when  the 
quotient,  for  a  genuine  coin,  would  be  lo^.  Of  course,  if 
the  coin  be  new,  it  will  be  sufficient  to  ascertain  that  it 
weighs  just  as  much  as  a  good  florin,  and  is  of  exactly  the 
same  diameter  and  thickness,  which  are  readily  measured  by 
cutting  a  slit  in  a  piece  of  cardboard  through  which  a  new 
florin  will  exactly  pass. 

Standard  silver  is  whitened  by  being  heated  until  the 
oxygen  of  the  air  has  converted  a  little  of  the  copper  at  the 
surface  into  oxide  of  copper,  which  is  dissolved  off  by  im 
mersing  the  metal  in  weak  vitriol  (diluted  sulphuric  acid) 
or  in  ammonia,  or  by  boiling  it  in  a  solution  of  cream  of 
tartar  and  common  salt.  The  film  of  nearly  pure  silver 
which  then  remains  at  the  surface  exhibits  a  want  of  lustre 
and  is  called  dead  or  frosted  silver.  It  is  brightened  by 
burnishing. 

Oxidised  silver,  as  it  is  erroneously  called,  is  made  by 
immersing  articles  of  silver  in  a  solution  obtained  by  boiling 
sulphur  with  potash,  when  the  metal  becomes  coated  with  a 
thin  film  of  sulphuret  of  silver. 

The  tarnish  which  is  produced  upon  the  surface  of  silver 
when  exposed  to  air  is  also  due  to  the  formation  of  a  coating 
of  sulphuret  of  silver  by  the  action  of  sulphuretted  hydrogen ; 


234      Metals:  their  Properties  and  Treatment. 

the  sulphuret  of  silver  is  itself  black,  but  a  thin  film  of  it 
upon  the  surface  of  the  metal  often  exhibits  the  rainbow 
colours  caused  by  the  decomposition  of  the  light  reflected 
through  it.  Tarnished  silver  is  most  readily  cleaned  with  a 
solution  of  cyanide  of  potassium,  but  this  salt  is  so  fatally 
poisonous  that  its  general  use  should  be  discouraged.  Am 
monia  (hartshorn)  will  also  remove. the  film  of  sulphuret  of 
silver  if  assisted  by  friction. 

Plated  articles  are  made  of  an  alloy  of  copper  and  brass 
coated  with  silver.  The  brass  having  been  melted  with  the 
requisite  proportion  of  copper  in  a  black-lead  crucible,  is 
cast  into  bars  3  inches  broad,  \\  inch  thick  and  18  or  20 
inches  long.  The  two  faces  of  the  bar  are  carefully  smoothed 
with  a  file,  and  a  plate  of  silver  ^5th  inch  thick,  and  some 
what  shorter  than  the  bar,  is  laid  upon  each  face  and  tied 
with  iron  wire.  A  little  saturated  solution  of  borax  is  allowed 
to  run  in  round  the  edges,  in  order  that  this  salt  may  melt 
and  dissolve  the  oxide  off  the  surface  of  the  brass  when 
heated  in  the  furnace.  The  bar  is  now  laid  upon  a  coke 
fire  and  heated  until  the  surfaces  of  brass  and  silver  have 
contracted  a  firm  adhesion,  when  the  compound  bar  is  ready 
for  the  rolling  mill.  After  rolling,  it  is  cleaned  with  diluted 
sulphuric  acid.  Sometimes  the  clean  copper  surface  is 
wasljed  over  with  solution  of  nitrate  of  silver  before  applying 
the  plate  of  silver.  A  thin  film  of  silver  would  then  be 
chemically  deposited  upon  the  surface  of  the  copper  and 
would  both  prevent  oxidation  and  favour  the  adhesion  of 
the  silver  plate. 

The  plated 'wire  used  for  making  toast-racks,  &c.,  is  made  of 
copper  coated  with  silver.  The  strip  of  silver  is  bent  round 
into  the  form  of  a  hollow  cylinder,  its  edges  somewhat  over 
lapping;  a  red-hot  cylinder  of  copper  is  thrust  into  this,  and 
the  edges  of  the  silver  are  joined  together  by  rubbing  with 
a  steel  burnisher.  The  copper  core  is  then  withdrawn,  the 
tube  of  silver  thoroughly  cleaned  inside,  and  slipped  upon  a 
bright  copper  rod  so  as  to  fit  closely,  leaving  the  ends  of  the 


Electro-plating,  235 

copper  somewhat  projecting.  Grooves  are  made  in  these 
ends,  into  which  the  silver  is  forced  down,  so  as  to  exclude 
the  air  from  the  copper  surface  inside.  The  cylinder  is 
made  red  hot  and  well  rubbed  with  a  steel  burnisher,  until 
the  silver  thoroughly  adheres  to  the  copper,  which  is  then 
drawn  into  wire. 

Electro-plating  is  now  very  generally  employed  for  coating 
articles  of  baser  metal  with  a  film  of  silver.  This  art  consists 
in  decomposing  a  solution  containing  silver,  with  the  aid  of 
a  galvanic  battery,  in  such  a  manner  that  the  metal  may  be 
deposited  upon  the  surface  of  the  article  to  be  plated; 
German  silver  (p.  173)  is  generally  employed  as  the  material 


FIG.  86. — Process  of  Electro-plating. 

for  the  latter,  the  articles  being  then  said  to  be  electro-plated 
on  white  metal.  They  must  be  thoroughly  cleaned  by  boiling 
them  with  soda,  washing  with  water,  and  dipping  into  very 
weak  aquafortis  (dilute  nitric  acid)  to  take  off  the  film  of 
oxide ;  they  are  afterwards  washed,  scoured  with  sand,  again 
dipped  in  the  weak  acid,  and  finally  rinsed  in  water. 

The  articles  to  be  electro-plated  are  suspended  by  stout 
copper  wires  (Fig.  86)  in  a  vessel  of  wood  or  earthenware 
containing  a  solution  of  cyanide  of  silver  in  cyanide  of 
potassium,  of  which  every  gallon  contains  an  ounce  of  silver. 
The  suspending  wires  are  connected  by  stout  copper  wires 
with  the  last  zinc  plate  of  a  galvanic  battery  consisting  of 


236      Metals :  their  Properties  a; id  Treatment. 

alternate  plates  of  zinc  and  copper  immersed  in  diluted 
sulphuric  acid ;  the  last  copper  plate  of  this  battery  is  con 
nected  with  a  series  of  silver  plates  suspended  in  the  silvering 
liquid  opposite  to  the  articles  to  be  coated.  The  galvanic 
influence  (or  current}  transmitted  from  the  battery  causes  the 
decomposition  of  the  cyanide  of  silver  in  the  solution,  the 
silver  being  deposited  upon  the  articles  to  be  plated,  and 
the  cyanogen,  which  was  combined  with  the  silver  in  the 
liquid,  uniting  with  the  silver  upon  the  plates  of  that  metal 
and  forming  a  fresh  quantity  of  the  cyanide  of  silver  equal 
to  that  which  has  been  decomposed ;  this  dissolves  in  the 
liquid  and  always  maintains  it  of  the  same  strength.  The 
articles  are  weighed  before  and  after  plating,  in  order  to 
ascertain  the  amount  of  silver  which  has  been  deposited 
upon  them ;  it  usually  amounts  to  about  an  ounce  and  a  half 
upon  a  square  foot  of  surface. 

In  order  to  secure  the  perfect  adhesion  of  the  film  of 
silver,  the  objects  to  be  plated  are  sometimes  dipped  into  a 
solution  of  nitrate  of  mercury  until  they  are  covered  with  a 
thin  coating  of  that  metal,  before  they  are  immersed  in  the 
silvering-bath.  They  are  then  struck  by  placing  them  in 
the  silvering  liquid  and  connecting  them  with  the  zinc  of  a 
strong  battery  for  a  short  time,  after  which  they  are  brushed 
with  fine  sand  to  show  that  the  coating  is  perfect,  and  the 
process  of  silvering  is  then  proceeded  with. 

To  preserve  the  silvering  solution  of  uniform  strength, 
the  articles  to  be  plated  are  sometimes  kept  in  motion  by 
attaching  the  connecting  rods  to  a  frame  furnished  with 
wheels  which  travel  along  a  rail  on  the  edge  of  a  vat,  and 
are  moved  by  clock-work  or  steam-power. 

The  deposit  of  silver  is  without  lustre  and  requires  bur 
nishing.  It  is  dried  by  immersing  the  article  in  boiling 
distilled  water,  and  allowing  it  to  dry  by  its  own  heat  when 
removed.  When  a  lustrous  deposit  is  required,  one  gallon 
of  the  silvering  liquid  is  mixed  with  six  ounces  of  a  liquid 
called  bisulphide  of  carbon  and  set  aside  for  twenty-four 


Dry  Silvering.  237 

hours.  Two  ounces  of  this  solution  are  added  to  twenty 
gallons  of  the  silvering  liquid,  and  left  for  twelve  hours 
before  use.  The  action  of  the  bisulphide  of  carbon  in 
causing  a  lustrous  deposit  has  not  yet  received  a  satisfactory 
explanation. 

Silvering  for  merely  Ornamental  Purposes. — Where  a  very 
thin  film  of  silver  only  is  required,  as  for  articles  not  sub 
jected  to  much  wear,  advantage  is  taken  of  the  great 
malleability  of  this  metal,  in  which  it  is  surpassed  only  by 
gold,  to  beat  it  out  into  exceedingly  thin  leaves,  which  are 
applied  to  the  surface  to  be  silvered.  The  silver  leaf  is 
manufactured  in  the  same  manner  as  gold  leaf,  to  which  the 
reader  may  refer.  It  is  applied  to  non-metallic  objects  with 
some  adhesive  liquid,  such  as  gum  or  size.  In  covering 
metallic  objects  with  silver  leaf,  they  are  heated  to  remove 
grease,  and  plunged  into  weak  aquafortis  to  dissolve  off  the 
oxide.  The  surface  is  next  scoured  with  wet  pumice  stone, 
warmed,  and  again  dipped  in  weak  aquafortis,  to  roughen 
it,  so  that  the  silver  leaf  may  more  readily  cling  to  it. 
If  necessary,  the  surface  is  further  roughened  by  hatching 
with  a  graving  tool.  The  metal  is  then  carefully  heated  till 
a  thin  film  of  oxide  causes  it  to  assume  a  bluish  tint,  the 
leaves  of  silver  applied  in  successive  layers,  and  well  fixed  by 
a  burnisher  of  steel,  the  object  being  heated  again  before 
every  application  of  the  silver. 

The  process  of  dry  silvering  upon  copper  and  brass,  which 
is  now  seldom  followed,  consisted  in  applying  to  the  clean 
surface  an  amalgam  of  silver  from  which  the  mercury  is 
afterwards  expelled  by  heat.  A  pasty  amalgam  is  made  by 
dissolving  silver  in  about  six  times  its  weight  of  mercury. 
The  amalgam  is  applied  with  a  brush  made  of  brass  wire 
dipped  into  a  solution  of  nitrate  of  mercury,  which,  being 
decomposed  by  the  copper  and  zinc  of  the  brass,  deposits  a 
coating  of  mercury  upon  the  brush  to  which  the  silver- 
amalgam  then  readily  adheres.  The  article  is  then  mode- 
ra'ely  heated  to  expel  the  mercury  in  vapour,  when  a  dead 


238      ]\Ietals :  tJicir  Properties  and  Treatment, 

film  of  silver  is  left  upon  the  surface,  which  is  afterwards 
burnished. 

For  silvering  flat  surfaces,  such  as  the  scales  of  barometers, 
the  chloride  of  silver  is  employed.  To  prepare  this,  a  piece 
of  standard  silver  is  dissolved  in  a  glass  or  earthen  vessel, 
with  the  aid  of  heat,  in  aquafortis  (diluted  nitric  acid).  If 
any  dark  powder  remains  undissolved,  it  consists  of  finely 
divided  gold,  which  is  often  found  in  old  silver.  The  solu 
tion,  which  contains  nitrate  of  silver  and  nitrate  of  copper,  is 
mixed  with  common  salt  dissolved  in  water.  The  chloride 
of  sodium  (common  salt)  decomposes  the  nitrate  of  silver, 
forming  nitrate  of  sodium,  and  chloride  of  silver,  which 
separates  as  a  white  curdy  precipitate.  The  liquid  is  well 
stirred,  the  chloride  of  silver  allowed  to  settle  down,  the 
liquid  poured  off  and  replaced  by  fresh  water  ;  after  this  has 
been  repeated  several  limes,  the  washed  chloride  of  silver  is 
dried  in  an  oven,  and  finely  powdered.  One  part  of  the 
powder  is  mixed  wiih  three  parts  of  pearlash,  one  part  of 
.chalk,  and  one-and-a-half  of  salt.  The  surface  of  the  copper 
or  brass  to  be  silvered  is  rubbed  with  a  wet  cork  or  leather 
dipped  in  this  mixture,  when  the  metal  decomposes  the 
chloride  of  silver,  forming  chloride  of  copper,  and,  in 
the  case  of  brass,  chloride  of  zinc,  and  metallic  silver  is 
deposited. 

A  mixture  of  the  chloride  of  silver  with  ten  parts  of  cream 
of  tartar  is  said  to  answer  the  same  purpose. 

Silvering  on  glass  is  effected  by  precipitating  silver  from  a 
solution,  in  contact  with  the  glass,  by  certain  chemical 
agents,  and  being  a  purely  chemical  process,  will  not  be 
considered  here.  Looking-glasses  are  silvered  with  an 
•amalgam  of  tin  (see  Mercury). 


Occurrence  of  Gold  in  Nature.  239 


GOLD. 

There  is  no  positive  evidence  that  gold  exists  in  Nature 
in  any  other  than  the  metallic  state,  though  it  is  believed  by 
some  to  exist  as  a  sulphuret  in  some  varieties  of  pyrites. 
There  are  fe\v  regions  in  which  small  quantities  of  this  metal 
cannot  be  discovered,  though  in  the  great  majority  of  cases 
its  quantity  is  too  small  to  pay  for  the  labour  of  separating 
it  from  the  other  matters  with  which  it  is  associated. 

In  England,  small  quantities  of  gold  are  found  in  the 
Cornish  alluvial  deposits  which  furnish  the  stream  tin  ore. 
In  Wales,  it  has  been  found  near  Dolgelly.  Ireland  has 
furnished  gold  from  Wicklow,  where  it  is  found  scantily 
distributed  through  sands  in  the  form  of  gold-dust,  and  very 
rarely  in  small  rounded  fragments  or  nuggets.  In  Scotland, 
the  precious  metal  has  been  traced  in  Perthshire,  and,  very 
recently,  considerable  quantities  of  it  have  been  extracted  in 
Sutherlandshire. 

On  the  continent  of  Europe,  the  gold  mir.es  of  Hungary 
and. Transylvania  are  the  most  important.  At  Konigsberg, 
the  metallic  gold  is  disseminated  through  sulphuret  of  silver. 

In  Sweden,  gold  is  found  associated  with  pyrites  at 
Edelfors  in  Smoland. 

The  sands  of  the  Rhine  contain  minute  quantities  of  gold 
for  which  they  are  sometimes  washed  when  work  is  scarce, 
although  about  eight  million  parts  of  'sand  must  be  washed 
for  one  part  of  gold. 

In  Spain,  the  province  of  Asturias  formerly  furnished  a 
considerable  quantity  of  gold,  but  the  workings  are  now 
neglected. 

Italy  is  by  no  means  destitute  of  gold.  Veins  of  pyrites 
containing  gold  are  found  in  a  granitic  rock  at  the  foot  of 
Monte  Rosa.  The  sands  of  some  of  the  rivers  on  the 
southern  slopes  of  the  Alps  also  furnish  gold. 


240       Metals  :  their  Properties  and  Treatment. 

Siberia  yields  gold  distributed  through  hornstone,  a  variety 
of  quartz.  The  sands  of  Siberian  rivers  are  not  considered 
to  be  worth  washing  if  they  contain  less  than  one  part  of 
gold  in  a  million. 

The  Ural  mountains  contain  some  rich  gold  districts,  the 
metal  being  found  in  pyrites,  in  clay,  and  in  the  sands  of 
rivers. 

Japan,  Ceylon,  Borneo  and  Thibet  also  contribute  to  the 
supply  of  gold. 

Africa  seems  to  have  been  the  oldest  and  richest  of  the 
sources  of  gold.  Sofala,  on  the  coast  of  Cam-aria,  has  sands 
abounding  in  gold-dust,  and  is  reputed  to  have  been  the 
Ophir  of  the  ancients.  To  the  south  of  the  great  desert  of 
Sahara,  the  negroes  dig  but  earth  rich  in  gold-dust  to  a  con 
siderable  depth. 

In  modern  times,  down  to  about  the  year  1850,  Brazil, 
Chili,  Peru  and  Mexico  purveyed  most  of  the  gold  employed 
throughout  the  world.  Minas  Geraes  in  Brazil  was  a  cele 
brated  auriferous  district. 

But  the  discoveries  of  gold  in  California  and  Australia, 
which  are  yet  fresh  in  the  memory  of  the  present  generation, 
have  immensely  increased  the  supplies  of  the  metal.  In 
California,  the  gold  is  chiefly  alluvial  gold,  being  found  in 
the  alluvial  deposits  formed  by  the  Sacramento  and  other 
rivers.  In  Australia,  gold-quartz  is  more  common,  the  metal 
being  disseminated  in  thin  plates,  and  in  branch-like  frag 
ments,  through  lumps  of  quartz-rock.  It  is  also  abundant, 
in  the  form  of  gold-dust  and  nuggets,  in  the  alluvial  forma 
tion  produced  by  the  crumbling  down  of  the  rocks  containing 
gold,  under  the  influence  of  torrents  which  have  carried  the 
gold,  together  with  clay  and  other  matters,  into  deep  gullies, 
at  the  bases  of  the  rocks,  where  the  alluvium  has  been  de 
posited  upon  a  bed  of  pipe-clay,  being  richest  in  gold  at  the 
lower  part  of  the  deposit,  on  account  of  the  great  weight  of 
the  metal. 

Native  gold  always  contains  silver,  and  generally  copper, 


Gold-washing.  24 1 

but  in  very  variable  proportions,  though  the  gold  from  the 
same  district  has  commonly  the  same  composition.  Aus 
tralian  gold  is  remarkably  pure. 

The  simplest  method  by  which  gold  is  extracted  is  that  of 
washing  the  alluvial  deposits,  the  sands  of  rivers,  &c.  There 
are  various  modes  of  effecting  this,  according  to  the  resources 
of  the  gold-washers,  but  in  all  cases  the  separation  of  the 
gold  from  the  earthy  matters  depends  upon  the  high  specific 
gravity  of  the  gold  (19*3),  the  lighter  earthy  matters  being 
carried  off  by  the  water. 

In  Africa,  the  deposits  containing  gold  are  washed  by  the 
negroes  in  the  shells  of  gourds,  being  well  stirred  up  with 
water,  which  is  poured  off  with  the  earthy  matters  suspended 
in  it,  leaving  the  gold  dust  in  minute  flattened  grains  at  the 
bottom.  The  gold  is  kept 
in  tubes  made  from  the 
quills  of  the  ostrich  or  vul 
ture. 

In  South  America,  the 
washing  is  conducted  in 
shallow  iron  or  zinc  pans  FIG.  87.— Gold-washing  Pan. 

(Fig.  87). 

Sometimes  the  deposits  are  thrown  upon  the  top  of  a 
sloping  plank  with  shallow  grooves  cut  across  it,  when  the 
grains  of  gold  settle  down  into  the  grooves,  and  the  earthy 
matters  are  carried  on  by  the  stream. 

Long  shallow  troughs  of  wood  are  employed  by  some 
gold-washers,  lined  at  the  bottom  with  coarse  baize,  or  with 
tanned  skins  with  the  hair  upwards.  The  grains  of  gold 
become  entangled  in  these,  and  when  the  earthy  matters 
have  been  washed  away,  the  linings  are  well  beaten  over  a 
tank  of  water  to  remove  the  gold. 

At  the  Californian  and  Australian  gold-diggings,  a  cradle 
(Fig.  88)  has  been  extensively  employed.  This  is  a  wooden 
trough  about  six  feet  long,  resting  upon  rockers.  At  the 
head  of  it  is  a  grating  upon  which  the  alluvial  deposit  to  be 

R 


242       Metals :  their  Properties  and  Treatment. 

washed  is  thrown.  This  end  of  the  cradle  is  about  four 
inches  higher  than  the  other,  so  that  a  stream  of  water  enter 
ing  it  flows  through  and  escapes  at  the  lower  end,  left  open 
for  this  purpose,  carrying  the  earthy  matters  with  it,  leaving 
the  particles  of  gold,  with  a  small  quantity  of  earthy  matter, 
in  the  trough.  These  are  swept  out  into  a  pan,  dried  in  the 
sun,  and  freed  from  the  lighter  matters  by  blowing  upon 
them. 

In  the  gold  washings  of  the  Ural  Mountains,  the  sands 
are  thrown  into  boxes  the  bottoms  of  which  are  made  of 


FIG.  88. — Cradle  for  Gold-washing. 

perforated  iron  plates.  These  boxes  are  placed  under  a  fall 
of  water,  in  which  the  sands  are  stirred  up  with  a  shovel. 
The  fine  sand  and  gold  dust  are  washed  through  on  to 
sloping  boards  covered  with  baize,  a  workman  being  engaged 
in  sweeping  the  deposit  up  the  inclined  plane  with  a  heather 
broom.  After  a  second  washing  on  a  smaller  inclined  table, 
the  particles  of  magnetic  iron  ore  are  extracted  by  a  magnet, 
and  the  gold  dust  is  melted  in  a  plumbago  crucible,  when 
the  earthy  matters  remain  upon  the  surface  of  the  melted 
gold. 


Extraction  of  Gold.  243 

At  some  of  the  Russian  works,  the  sifting  of  the  sands  is 
effected  in  cylinders  of  perforated  sheet  iron,  which  are 
placed  in  a  sloping  position  above  the  washing  tables,  and 
made  to  rotate  upon  an  axis.  A  stream  of  water  being  let 
in  at  the  upper  end,  carries  the  sand  and  gold  dust  through 
the  perforations  on  to  the  sloping  tables,  while  the  large 
pebbles  pass  out  at  the  lower  end  of  the  cylinder. 

The  boxes  in  which  the  more  tenacious  alluvial  deposits 
are  mixed  with  water  are  sometimes  provided  with  agitators 
worked  by  horse  or  steam  power,  and  having  knives  attached 
for  breaking  up  and  mixing  the  deposits. 

When  the  gold  is  disseminated  through  quartz  or  some 
similar  rock,  this  must  be  crushed  in  order  to  extract  the 
gold,  an  operation  attended  with  great  expense,  on  account 
of  the  hardness  of  the  rock.  Where  it  is  possible,  the  rock 
is  rendered  more  brittle  by  being  heated  to  redness  and 
quenched  with  water.  The  crushing  is  effected  either  by 
passing  the  gold-quartz  between  chilled  cast-iron  rollers,  or 
by  means  of  stampers  similar  to  those  employed  in  the 
Cornish  tin-works. 

From  the  stamped  ores,  as  well  as  from  the  auriferous 
sands  which  have  been  concentrated  by  washing,  the  gold  is 
sometimes  extracted  by  a  process  of  amalgamation  similar  to 
that  employed  in  the  case  of  silver. 

As  practised  by  the  Mexican  gold-washers,  the  process  of 
amalgamation  consists  in  shaking  the  damp  gold-dust,  still 
mixed  with  foreign  matters,  with  metallic  mercury  which 
dissolves  the  gold.  The  impurities  having  been  washed 
away,  the  amalgam  is  squeezed  in  a  cloth,  when  about  half 
the  mercury  flows  out,  and  the  solid  amalgam  remaining  in 
the  cloth  is  placed  in  a  small  iron  dish,  covered  up  with 
green  leaves  and  set  over  a  charcoal  fire ;  a  good  deal  of  the 
mercury  vapour  is  condensed  in  the  leaves,  which  are  re 
newed  from  time  to  time  as  they  get  dry. 

In  the  Tyrol,  particles  of  gold  exist  disseminated  through 
iron  pyrites,  from  which  they  are  extracted  by  amalgamation. 

R  2 


244      Metals :  their  Properties  and  Treatment. 

The  amalgamating  mill  (Fig.  89)  is  a  large  cast-iron  dish  (e) 
firmly  fixed  upon  a  wooden  table.  In  this  dish  there  is  a 
heavy  cone  of  hard  wood  (m)  of  the  same  shape  as  the  dish, 
and  just  large  enough  to  leave  an  interval  of  half-an-inch 
between  them;  several  projecting  iron  ribs  are  fixed  to  the 
under  side  of  this  cone,  which  nearly  touch  the  bottom  of 
the  pan,  and  the  upper  surface  of  the  cone  is  hollowed  out 
so  as  to  form  a  shallow  funnel .  The  wooden  cone  is  con 
nected  with  an  axle  (a),  so  that  it  may  be  made  to  revolve 
at  the  rate  of  about  twenty  turns  a  minute.  About  50  Ibs. 
of  mercury  having  been  poured  into  the  iron  pan,  the 


FIG.  89.— Mill  for  amalgamating  Pyrites  containing  Gold,     r  r1,  Toothed 
wheels  for  transmitting  motion  to  the  axle  a  b. 

auriferous  pyrites,  previously  stamped  or  ground  to  a  fine 
powder,  is  brought  into  the  mill  by  a  stream  of  water  from 
the  spout  (G),  when  it  is  thoroughly  stirred  with  the  mercury 
by  the  projecting  ridges  at  the  bottom  of  the  wooden  cone. 
In  order  that  no  gold  may  escape  being  dissolved  by  the 
mercury,  the  pyrites  which  has  been  treated  in  one  mill 
flows  out  through  a  spout  (G)  into  the  next,  and  so  on  through 
an  entire  series.  After  about  a  month,  the  mercury  is 
drawn  off  and  squeezed  through  wash-leather,  which  allows 
the  liquid  portion  to  pass  through,  and  retains  a  soft  solid 
amalgam  containing  about  one-third  of  its  weight  of  gold, 


Extraction  of  Gold. 


245 


from  which  the  mercury  is  separated  by  distillation  in  the 
apparatus  represented  in  Fig.  90. 

For  the  extraction  of  gold  from  gold-quartz,  lead  has  been 
employed  with  great  advantage,  since  this  metal,  when 
melted,  will  dissolve  gold  just  as  mercury  will  at  the  ordinary 
temperature.  The  crushed  quartz  is  fluxed  by  an  addition 
of  lime  and  clay  (see  Iron),  with  which  is  added  either 
metallic  lead  or  galena  (sulphuret  of  lead),  or  even  rich 


FIG.  90.— Apparatus  for  distilling  the  Amalgam  of  Gold,     a,  Dishes  for  re 


ceiving  the  amalgam,  attached  to  the  pillar  b.     A,  Iron  cylinder  heated 
by  a  fire  on  the  grate  c.     d,  Ire 
f,  Tube  for  vapour  of  mercury. 


on  the  grate  c.     d,  Iron  dome.  .  e,  Iron  cover  of  the  furnace. 


Cylinder  in  which  the  mercury 

"condenses,  closed  by  an  iron  plate  h  and  a  wooden  plug  i.     k,  Water- 
tank.     /,  Vessel  for  collecting  the  mercury,     m,  Chimney. 

lead  slags,  with  some  coal  or  charcoal  to  reduce  the  lead 
to  the  metallic  state. 

The  lead  containing  gold  (and  silver)  is  then  subjected  to 
the  process  of  cupellation  (p.  208). 

In  Hungary,  gold  is  extracted  from  iron  pyrites  associated 
with  quartz,  by  taking  advantage  of  the  property  of  dissolv 
ing  gold  possessed  by  sulphuret  of  iron.  The  pyrites  is 


246      Metals :  their  Properties  and  Treatment. 

roasted  in  heaps  with  brushwood,  to  convert  a  part  of  the  bi- 
sulphuret  of  iron  into  oxide  of  iron,  and  a  part  into  suiphuret 
of  iron.  The  roasted  ore  is  fused  with  an  addition  of  lime, 
when  a  slag  is  formed  by  the  combination  of  the  silica  (quartz), 
the  oxide  of  iron,  and  the  lime,  whilst  the  suiphuret  of  iron 
fuses,  dissolves  the  gold,  and  forms  a  matt  beneath  the 
slag. 

This  suiphuret  of  iron  is  roasted  so  as  to  convert  it  into 
oxide,  and  fused  with  a  fresh  quantity  of  the  auriferous 
pyrites  and  the  requisite  proportion  of  lime,  when  a  fresh 
quantity  of  the  matt  will  be  obtained,  containing  the  gold 
from  the  two  charges  of  pyrites.  This  operation  is  repeated 
until  a  sufficient  quantity  of  gold  has  accumulated  in  the 
matt  of  suiphuret  of  iron,  which  is  then  melted  down  with 
lead  ;  this  metal  extracts  the  gold  from  the  suiphuret  of  iron, 
and  the  latter  remains  in  a  melted  state  upon  the  surface  of 
the  lead.  The  lead  is  afterwards  cupelled  in  order  to  extract 
the  gold,  and  since  lead  containing  silver  is  generally 
employed,  this  metal  is  left  on  the  cupel  alloyed  with  the 
gold. 

Whenever  ores  of  copper,  lead,  or  silver  contain  gold,  the 
latter  is  always  present  in  the  metal  extracted  from  them, 
and  is  recovered  from  those  metals  by  the  processes  de 
scribed  in  the  article  on  Silver. 

In  order  to  separate  the  gold  from  the  silver  with  which  it 
is  commonly  alloyed,  whether  it  has  been  obtained  by  wash 
ing,  or  by  any  of  the  above  processes  of  extraction,  the  alloy 
of  silver  and  gold  is  heated  with  sulphuric  acid,  which  con 
verts  the  silver  into  sulphate  of  silver,  capable  of  being  dis 
solved  by  water,  and  leaves  the  gold  untouched. 

Parting  by  Sulphuric  Add. — The  alloy  of  silver  and  gold, 
in  which,  of  course,  the  former  metal  always  predominates, 
is  melted  either  in  wrought-iron  or  plumbago  crucibles,  and 
poured  into  water  in  order  to  granulate  it  or  divide  it  into  a 
flaky  condition,  exposing  a  large  surface  to  the  action  of  the 
acid.  The  granulated  metal  is  dried,  weighed,  and  boiled 


Parting  by  Sulphuric  Acid.  247 

with  oil  of  vitriol  (concentrated  sulphuric  acid).  When  the 
alloy  is  rich  in  gold,  the  operation  is  performed  in  platinum 
alembics  or  stills,  but  in  the  more  common  case,  where  the 
silver  contains  only  a  few  grains  of  gold  in  the  pound,  cast- 
iron  pans  are  employed ;  each  pan  (about  two  feet  wide)  has 
an  iron  lid,  from  which  a  bent  pipe  passes  down  into  an  air 
tight  leaden  tank,  where  the  vapour  of  sulphuric  acid  which 
escapes  during  the  boiling  may  be  condensed.  A  large 
quantity  of  sulphurous  acid  gas  passes  off  during  the  opera 
tion,  and  this  is  conducted,  from  the  leaden  tank,  by  a  pipe 
of  the  same  metal,  into  a  large  leaden  chamber,  30  feet  long 
by  10  feet  wide,  and  6  feet  high,  in  which  it  is  reconverted, 
by  an  appropriate  chemical  process,  into  oil  of  vitriol,  which 
is  used  over  again. 

One  fire  is  made  to  heat  two  of  the  iron  pots,  in  which  the 
granulated  silver  is  placed,  together  with  twice  its  weight  of 
concentrated  sulphuric  acid,  which  is  gently  boiled  until  the 
silver  is  entirely  converted  into  sulphate  of  silver,  forming  a 
pasty  mass  consisting  of  minute  crystals.  This  is  taken  out 
by  cast-iron  ladles,  and  thrown  into  leaden  cisterns,  where  it 
is  stirred  up  with  water,  and  boiled  by  passing  steam  into  it 
through  perforated  leaden  pipes  connected  with  a  boiler. 
The  boiling  water  dissolves  the  sulphate  of  silver,  and  the 
finely-divided  gold  is  left  as  a  black  powder,  which,  when 
accumulated  in  sufficient  quantity,  is  well  washed  and  dried. 
It  still  retains  a  small  proportion,  varying  from  ^Vth  to  5Vtn 
of  its  weight,  of  silver. 

The  solution  of  sulphate  of  silver  is  drawn  off,  by  leaden 
siphons,  into  leaden  troughs,  where  it  is  left  in  contact  with 
shavings  of  copper.  This  metal  enters  into  solution,  form 
ing  sulphate  of  copper,  and  separating  the  silver  in  a  finely- 
divided  state,  as  a  grey  powder  ;  this  is  allowed  to  settle 
down,  the  solution  of  sulphate  of  copper  run  off  into  another 
cistern,  and  the  silver  washed  with  fresh  water,  drained,  and 
compressed  by  hydraulic  pressure,  in  a  square  cast-iron  box, 
which  makes  it  into  cakes  of  60  Ibs.  each.  These  are  dried, 


248      Metals :  their  Properties  and  Treatment. 

melted  in  plumbago  crucibles,  and  cast  into  ingots.  Cast- 
iron  crucibles  strengthened  by  shrinking  hot  iron  hoops 
upon  the  cold  crucibles  are  sometimes  employed,  but  since 
they  become  impregnated  with  silver,  the  latter  must  be 
extracted  by  melting  some  lead  in  them  when  they  are  worn 
out. 

The  solution  of  sulphate  of  copper  formed  in  displacing 
the  silver  by  copper  is  evaporated  in  shallow  leaden  pans,  to 
a  proper  strength,  and  the  sulphate  of  copper  allowed  to 
crystallise  out  on  cooling.  The  liquid  remaining  after  the 
last  crystals  have  separated  contains  the  excess  of  sulphuric 
acid  which  has  been  employed  in  the  process,  very  little 
sulphate  of  copper  being  left  in  it,  because  this  salt  is  almost 
insoluble  in  moderately  strong  sulphuric  acid.  This  liquor 
is  boiled  down  in  a  platinum  still,  until  the  water  has 
boiled  away,  and  the  concentrated  sulphuric  acid  is  left  in 
the  still,  ready  to  be  employed  for  the  treatment  of  a  fresh 
quantity  of  silver. 

The  sulphate  of  copper  (blue  vitriol)  obtained  in  this  pro 
cess  is  a  salt  for  which  there  is  a  considerable  demand ;  it  is 
largely  used  for  dressing  grain  intended  for  seed,  to  prevent 
smut  It  is  also  employed  in  dyeing  and  calico-printing, 
and  in  many  other  branches  of  industry,  as  well  as  in  several 
forms  of  galvanic  battery. 

When  there  is  no  market  for  the  sulphate  of  copper,  the 
solution  of  the  salt  is  decomposed  by  scrap  iron,  as  in  the 
case  of  the  blue  water  at  Anglesea  (p.  128),  to  recover  the 
metallic  copper. 

In  such  works  for  the  refining  of  gold  and  silver,  the  pro 
cesses  can  be  conducted  economically  only  when  great  care 
is  taken  to  avoid  the  loss  of  any  particles  of  the  precious 
metals.  Thus  all  the  old  crucibles  are  ground  and  treated 
with  mercury  in  the  amalgamation  mill,  and  after  as  much 
gold  and  silver  as  possible  have  been  thus  extracted,  the 
residues  are  sold  to  the  sweep-washers,  who  extract  a  little 
more  by  melting  with  lead.  The  very  dust  off  the  floors  is 


Parting  by  Nitric  Acid.  249 

collected  and  treated  in  a  similar  manner.  One  part  of  gold 
can  be  profitably  extracted  from  2,000  parts  of  alloy  by  this 
process  of  parting  by  sulphuric  acid.  Its  introduction  has 
affected  the  metallurgy  of  gold  in  the  same  way  as  Pattin- 
son's  process  did  that  of  silver,  much  old  silver  plate  having 
been  treated  by  it  for  the  sake  of  the  gold  which  had  not 
been  found  worth  extracting  by  the  older  and  more  expensive 
method  of  parting  by  nitric  acid. 

When  the  alloy  contains  copper  as  well  as  silver  and  gold, 
it  may  also  be  treated  in  the  same  way,  the  copper  being  re 
moved,  with  the  silver,  as  a  soluble  sulphate ;  but  the  pro 
cess  does  not  succeed  well  with  an  alloy  containing  more 
than  75  parts  of  copper  in  1,000,  so  that,  if  it  be  richer,  it 
is  either  melted  with  more  silver,  or  is  cupelled  with  lead 
(p.  208),  in  order  to  reduce  the  copper  to  the  right  propor 
tion. 

Nor  should  the  alloy  contain  more  than  one-fifth  of  its 
weight  of  gold,  or  the  sulphuric  acid  will  not  extract  the 
silver.  When  platinum  stills  are  employed  for  parting  by 
sulphuric  acid,  it  is  necessary  that  the  alloy  should  be  free 
from  lead  and  tin,  which  are  apt  to  melt  upon  the  bottom  of 
the  still  and  seriously  to  corrode  the  platinum. 

Parting  of  Gold  and  Silver  by  Nitric  Acid. — Silver  is  easily 
dissolved  by  nitric  acid  and  converted  into  nitrate  of  silver, 
but  this  acid,  if  pure,  does  not  attack  gold.  If  the  nitric 
acid  contains  chlorine,  however,  it  will  dissolve  some  of  the 
gold,  so  that  it  is  always  necessary  to  test  it  by  adding  a 
little  solution  of  nitrate  of  silver,  which  will  render  it  milky, 
from  the  separation  of  the  insoluble  chloride  of  silver,  if  any 
chlorine  be  present.  An  alloy  containing  more  than  one 
part  of  gold  to  three  parts  of  silver  is  very  little  affected  by 
nitric  acid,  so  that  it  becomes  necessary  to  fuse  very  rich 
alloys  with  so  much  silver  that  the  gold  shall  form  only  one- 
fourth  of  the  alloy ;  this  is  the  origin  of  the  term  inquartation 
or  quartation,  used  in  speaking  of  this  process. 

The  alloy,  in  a  granulated  state,  is  heated  with  twice  its 


2  50       Metals :  their  Properties  and  Treatment. 

weight  of  moderately  strong  nitric  acid  (sp.  gr.  1*32)  in  a 
still  made  of  platinum,  glass,  or  earthenware,  connected  with 
an  apparatus  for  condensing  the  vapours  of  nitric  acid  which 
pass  off.  Whilst  the  silver  is  being  dissolved,  a  large  quan 
tity  of  red  gas  is  evolved,  resulting  from  the  action  of  the 
silver  upon  the  nitric  acid,  and  when  this  is  no  longer  per 
ceived,  the  silver  is  known  to  be  dissolved.  The  still  is 
then  cooled,  the  solution  of  nitrate  of  silver  drawn  off,  and 
the  undissolved  gold  boiled  with  a  little  more  nitric  acid  to 
extract  any  remaining  silver.  It  is  then  washed  with  water, 
dried,  melted,  and  cast  into  an  ingot. 

In  order  to  recover  the  silver  from  the  nitrate,  hydro 
chloric  acid  is  cautiously  added,  so  as  to  separate  the  bulk 
of  the  silver  as  the  insoluble  chloride,  leaving  the  nitric  acid 
in  the  solution,  which  may  be  used  again,  if  care  be  taken  to 
leave  a  little  nitrate  of  silver  undecomposed  in  the  solution, 
so  as  to  ensure  the  absence  of  chlorine.  The  separated 
chloride  of  silver  is  washed  with  water,  moistened  with  sul 
phuric  acid,  and  some  bars  of  zinc  placed  in  it,  when 
chloride  of  zinc  is  formed  and  dissolved,  the  silver  being  left 
in  the  finely-divided  metallic  state.  The  rest  of  the  zinc  is 
then  taken  out,  the  silver  allowed  to  remain  in  contact  with 
dilute  sulphuric  acid  to  dissolve  any  particles  of  zinc,  then 
thoroughly  washed  with  water,  dried,  melted,  and  cast  into 
ingots. 

Refining  of  Gold. — The  gold  obtained  by  parting  with  sul 
phuric  acid  is  refined  by  mixing  it  with  one-fourth  of  its  weight 
of  dried  sulphate  of  soda,  and  treating  it,  in  an  iron  pan,  with 
oil  of  vitriol,  to  the  amount  of  three  parts  for  every  five  parts 
of  sulphate  of  soda.  Heat  is  applied  as  long  as  any  vapours  of 
sulphuric  acid  escape.  This  is  repeated  a  second  time,  but 
without  driving  off  the  whole  of  the  sulphuric  acid.  The 
mass  is  then  boiled  with  sulphuric  acid,  when  the  gold  alone 
is  left,  and  is  melted  with  a  little  saltpetre,  which  extracts 
a  little  platinum,  before  casting  it  into  an  ingot.  At  the 
Russian  mint,  the  re-melting  is  effected  in  a  small  reverbera- 


Extraction  of  Gold  in  the  wet  way.  251 

tory  furnace,  with  a  cavity  in  which  the  gold  collects.  The 
explanation  of  this  process  is  simply  that  the  sulphuric  acid 
combines  with  the  sulphate  of  soda,  and  may  then  be  raised 
to  a  higher  temperature  without  vaporising  than  is  possible 
with  uncombined  sulphuric  acid.  The  higher  temperature 
employed  enables  the  sulphuric  acid  to  attack  the  remainder 
of  the  silver.  (See  Addendum,  p.  xi.) 

Extraction  of  Gold  from  Gold-quartz  in  the  wet  way. — It 
has  been  proposed  to  avoid  the  expensive  process  of  amal 
gamation,  by  digesting  the  pulverised  gold-quartz  with  y^^th 
part  of  black  oxide  of  manganese  and  some  muriatic  acid,  in 
an  earthen  vessel,  for  twelve  hours,  when  chlorine  is  generated, 
which  dissolves  the  gold  in  the  form  of  chloride  of  gold,  from 
which  the  metal  may  be  separated  in  a  finely-divided  state 
by  adding  to  the  liquid  a  solution  of  copperas  (sulphate  of 
iron).  The  dark  powder  of  gold  thus  separated  is  washed 
with  water,  dried,  and  melted  down.  When  the  gold  con 
tains  much  silver,  common  salt  is  employed  to  dissolve  the 
chloride  of  silver,  which  would  otherwise  protect  the  gold 
from  the  action  of  the  chlorine. 

Planner's  Process,  which  was  employed  with  economy  for 
the  extraction  of  gold  from  the  abandoned  residues  of  roasted 
pyrites  at  Reichenstein,  in  Upper  Silesia,  containing  less  than 
i  oz.  of  gold  per  ton,  is  rather  a  chemical  than  a  metallurgical 
process,  and  consists  in  treating  the  fine  powder,  in  a  moist 
state,  with  chlorine  gas,  which  converts  the  gold  into  a  soluble 
chloride  ;  this  is  washed  out  with  water,  and  treated  with 
sulphuretted  hydrogen,  which  separates  the  gold  as  an 
insoluble  black  sulphuret,  leaving  the  iron,  &c.,  in  the  solu 
tion.  The  sulphuret  of  gold  is  heated  to  expel  a  part  of  the 
sulphur,  dissolved  in  a  mixture  of  hydrochloric  and  nitric 
acids,  and  separated  from  the  solution  in  the  pure  metallic 
state  by  sulphate  of  iron.  The  precipitated  gold  is  washed, 
and  melted  down  with  a  little  borax  and  saltpetre. 

Gold  dust  and  nuggets  of  gold  never  consist  of  the  pure 
metal,  but  always  contain  silver,  and  sometimes  copper  and 


252      Metals :  their  Properties  and  Treatment. 

small  quantities  of  other  metals,  such  as  antimony  and  bis 
muth.  Grains  of  platinum  and  its  allied  metals  are  also  very 
commonly  found  in  alluvial  gold.  The  purest  native  gold  has 
been  found  at  Giron,  in  New  Grenada,  containing  only -j-j-^th 
part  of  silver.  Some  Californian  gold  contains  as  much  as 
nine  parts  of  silver  and  nearly  one  part  of  copper  in  a  hun 
dred  parts.  Californian  gold  also  sometimes  contains  small 
grains  of  an  extremely  hard  alloy  of  osmium  and  iridium, 
which  occasion  great  injury  to  the  die  in  coining,  since  they 
remain  unchanged  when  the  gold  is  cast  into  ingots. 

At  the  American  mint,  the  Californian  gold,  which  con 
tains  about  -nnnrth  of  its  weight  of  the  osm-iridium  alloy,  is 
melted  with  thrice  its  weight  of  silver,  which  lowers  its 
specific  gravity,  and  allows  the  osm-iridium  to  settle  to  the 
bottom.  The  greater  part  of  the  melted  metal  is  ladled  out, 
leaving  the  rest  very  rich  in  osm-iridium  at  the  bottom.  This 
is  repeatedly  melted  with  silver,  by  which  the  proportion  of 
gold  is  still  further  diminished,  and  ultimately  the  mixture  of 
osm-iridium  with  silver  and  a  little  gold  is  boiled  with  sul 
phuric  acid,  which  extracts  the  silver,  leaving  the  osm- 
iridium  mixed  with  some  powdered  gold,  which  may  be 
removed  by  washing. 

When  gold  contains  platinum  or  palladium,  it  is  very 
much  lighter  in  colour.  These  metals  cannot  be  separated 
by  the  ordinary  refining  processes.  The  presence  of  lead 
or  antimony,  even  in  very  minute  proportion,  is  found  to 
render  gold  extremely  brittle. 

Perfectly  pure  or  fine  gold  is  nearly  as  soft  as  lead,  far  too 
soft  therefore  to  resist  the  wear  to  which  it  would  be  sub 
jected  in  coinage  and  gold  plate.  The  alloy  used  for  coin, 
in  England,  consists  of  1 1  parts  of  gold  and  i  part  of  copper, 
which  is  harder  and  more  fusible  than  pure  gold.  Formerly, 
the  gold  was  alloyed  with  silver,  or  with  silver  and  copper, 
and  this  latter  alloy  is  still  employed  by  goldsmiths.  The 
guinea  was  composed  of  1 1  parts  of  gold,  \  part  of  silver, 
and  \  part  of  copper.  The  specific  gravity  of  sovereign 


Testing  of  Gold.  253 

gold  is  17-157  (that  of  pure  gold  being  19-3).  The  safest 
method  of  ascertaining  whether  a  sovereign  is  genuine 
consists,  as  in  the  case  of  silver  coin  (p.  233),  in  showing 
that  it  has  the  same  size  and  weight  as  a  sovereign  known 
to  be  genuine.  A  new  sovereign  weighs  123^  grs.,  but 
it  is  a  legal  tender  as  long  as  it  is  not  less  than  122-^  grs. 
in  weight.  So  hard  is  the  alloy,  that  with  proper  wear,  a 
sovereign  will  circulate  for  eighteen  years  without  falling 
below  the  legal  standard. 

The  gold  coin  of  the  United  States  and  of  France  con 
tains  only  9  parts  of  gold  to  i  part  of  copper. 

The  fineness  or  purity  of  gold  is  commonly  expressed  by 
stating  how  many  carats  of  gold  are  present  in  24  carats  of 
the  alloy.  Thus  pure  gold  would  be  24  carats  fine ;  sovereign 
gold,  22  carats  fine. 

Fractions  of  a  carat  are  expressed  in  grains  (4  grains  are 
equal  to  i  carat)  and  eighths  of  a  grain ;  thus  French  gold 
coin  would  be  styled  of  21  carats  2-f  grs.  fine,  or  worse 
0  carat  if  grs.,  implying  that  it  contained  so  much  less  gold 
than  the  English  standard. 

The  fineness  may  of  course  be  judged  of,  as  in  the  case  of 
sovereign  gold,  from  the  specific  gravity,  since  the  specific 
gravities  of  silver  and  copper  (respectively,  10-5  and  8-9) 
are  so  much  lower  than  that  of  gold  (19*3).  But  this  test 
has  been  found  fallacious  in  a  case  where  bars  of  platinum 
(sp.  gr.  21*5)  were  coated  with  gold  and  sold  as  solid  ingots 
of  that  metal,  which  is  more  than  twice  the  price  of  platinum. 
Gold  of  1 8  carats  fine  has  the  specific  gravity  i6'8. 

The  goldsmith  or  pawnbroker  generally  tests  the  gold  by 
touching  its  surface  with  a  stopper  wetted  with  aquafortis 
(nitric  acid),  which  produces  a  green  stain  upon  the  metal 
when  a  very  large  proportion  of  copper  is  present,  nitrate  of 
copper  being  then  produced.  This  is,  at  best,  a  rough  test, 
and  would  of  course  fail  altogether  if  the  surface  only  of  the 
base  alloy  were  coated  with  fine  gold. 

The  use  of  the  touchstone  admits,  in  practised  hands,  of  a 


254      Metals :  their  Properties  and  Treatment. 

far  more  exact  determination  of  the  value  of  the  alloy,  and 
unless  it  be  pretty  thickly  coated  with  richer  metal,  decep 
tion  is  more  easily  detected.  The  touchstone  is  a  piece  of 
black  basalt,  or  even  of  black  slate,  over  which  the  gold  to  be 
tested  is  drawn  so  as  to  leave  a  streak  of  fine  particles  of 
the  metal  upon  the  surface ;  this  streak  of  course  remains 
untouched  when  moistened  with  nitric  acid,  but  if  a  streak 
of  any  base  alloy  (of  copper  and  zinc  for  example),  made  to 
imitate  gold,  be  made  upon  the  surface  of  the  touchstone, 
the  nitric  acid  will  immediately  dissolve  it. 

The  acid  employed  in  this  test  is  generally  mixed  with  a 
minute  proportion  of  hydrochloric  acid  (98  parts  by  weight 
of  nitric  acid,  of  sp.  gr.  i  -34,  2  parts  of  hydrochloric  acid,  of 
sp.  gr.  i  -173,  and  25  parts  of  water).  The  streak  is  not 
apparently  affected  by  the  acid  if  the  gold  is  not  below 
1 8  carats  fine;  by  making  several  streaks  in  succession,  or 
by  grinding  off  a  part  of  the  surface  upon  the  touchstone, 
any  error  arising  from  a  thin  external  coating  of  fine  gold 
may  be  avoided  ;  the  feather  of  a  pen,  or  a  glass  rod,  serves 
for  moistening  the  streaks  with  the  acid. 

In  order  to  determine  by  the  touchstone  the  proportion 
of  gold  which  is  present  in  the  alloy,  the  streak  is  compared 
with  that  made  by  a  series  of  touch-needles  composed  of 
alloys  containing  gradually  diminishing  quantities  of  gold. 
In  experienced  hands,  the  quantity  of  gold  may  thus  be 

ascertained  with  an  error  of 
not  more  than  one  part  in 
a  hundred. 

The  exact  assay  of  the 

FIG    i  —Cupel  alloys  of  gold  is  an  imita 

tion,  on  the  small  scale,  of 

the  metallurgic  processes  of  inquartation,,  cupellation  and 
parting.  A  weighed  quantity  of  the  alloy,  say  6  grs.,  is 
wrapped  in  a  piece  of  thin  paper  together  with  three  times 
its  weight  of  pure  silver,  and  added  to  twelve  times  its 
weight  of  pure  lead  already  melted  in  a  bone-ash  cupel 


Assay  of  Gold. 


255 


FIG.  92. — Muffle. 


(Fig.  91),  heated  in  a  muffle  (Fig.  92)  or  arched  clay  oven, 
with  slits  for  admitting  air,  which  is  placed  in  a  brisk  fire 
(Fig.  93).  The  lead  and  copper  are 
both  converted  into  oxides,  the  oxide 
of  copper  dissolving  in  the  oxide  of 
lead,  and  both  being  absorbed  by 
the  bone-ash.  After  the  brightening 
(p.  211)  the  alloy  of  silver  and  gold 
which  is  left  on  the  cupel  is  hammered 
flat,  annealed  by  heating  to  redness, 
rolled  out  thin,  coiled  up  into  the  form  of  a  tube,  and  boiled, 
first  with  weak  nitric  acid  (sp.  gr.  i'i8),  and  then  with  a 
stronger  acid  (sp.  gr.  1-28)  in  order  to  extract  the  silver;  the 
gold  is  left  in  the  form  of  a  little  tube  (cornette)  having  much 
the  appearance  of  red  earthenware.  It  is  well  washed  with 
water,  carefully  transferred  to  a  small  crucible  without 
breaking  it,  dried,  and  heated 
to  redness  in  the  muffle,  when 
it  shrinks,  and  assumes  the 
ordinary  appearance  of  gold. 
Its  weight  is  ascertained  by 
a  very  accurate  balance,  and 
multiplied  by  four  (six  grains 
having  been  assayed)  to  ex 
press  the  fineness  of  the  gold. 
To  avoid  errors,  the  exact 
assayer  commonly  passes  a 
proof  or  weighed  quantity  of 
pure  gold  through  the  same 
process,  at  the  same  time,  with 
the  addition  of  a  proportion 
of  copper  about  equal  to  that  in  the  alloy,  and  corrects  his 
assays  by  deducting  from  the  weight  of  the  gold  finally 
obtained  the  increase  which  the  pure  gold  was  found  to 
have  experienced  in  consequence  of  its  having  retained 
traces  of  lead,  silver  and  copper. 


FIG.  93. — Assay  by  Cupellation.  a,  Iron 
castors  on  which  the  furnace  moves. 
b,  Ash-pit,  c,  Damper,  d,  Grate. 
f,  Muffle  containing  the  cupels,  g, 
Mouth-plate,  h,  Fuel. 


256       Metals :  their  Properties  and  Treatment. 

The  alloy  of  copper  and  gold  is  much  redder  than  pure 
gold  ;  the  addition  of  silver  whitens  it,  and  its  surface  may 
be  brought  to  any  shade  of  gold  colour  by  heating  it  until  a 
portion  of  the  copper  is  oxidised,  and  dissolving  out  this 
oxide  with  an  acid.  Goldsmiths  commonly  colour  their  gold 
by  boiling  it  for  twenty  minutes  with  a  mixture  of  i  part  of 
common  salt,  2  parts  of  saltpetre,  i  .part  of  alum  and  4  parts 
of  water,  the  mutual  action  of  which  would  result  in  the 
production  of  a  little  hydrochloric  acid  (from  the  chloride  of 
sodium,  common  salt),  and  a.  little  nitric  acid  (from  the  salt 
petre,  nitrate  of  potash) ;  this  pickle  dissolves  not  only  the 
copper,  but  some  of  the  gold,  which  is  recovered  by  pre 
cipitating  it  with  solution  of  copperas  (p.  251). 

The  great  value  of  gold,  and  its  perfect  freedom  from 
alteration  by  exposure  to  the  .atmosphere,  have  led  to  many 
devices  for  making  the  smallest  quantity  of  the  precious 
metal  cover  the  greatest  extent  of  surface,  by  taking  advantage 
of  its  extreme  malleability  and  ductility,  in  which  it  far  sur 
passes  all  other  metals. 

Gold-beating. — Pure  gold  may  be  extended  by  hammering 
so  as  to  present  a  surface  650,000  times  as  large  as  it 
originally  possessed,  but  for  this  purpose  it  must  be  per 
fectly  pure  or  fine  gold,  a  very  small  quantity  of  any  other 
metal  materially  injuring  its  malleability.  Gold  alloyed  with 
copper  or  silver  is,  however,  often  beaten  into  moderately 
thin  leaves,  when  a  colour  different  from  that  of  fine  gold  is 
required,  but  it  is  of  course  much  more  liable  to  tarnish. 
Dentists'  leaf  gold  for  stopping  teeth  is  generally  beaten 
from  fine  gold,  because  it  is  more  easily  pressed  into  a  com 
pact  form. 

The  gold  is  melted  in  a  crucible  with  a  little  borax,  which 
prevents  it  from  sticking  to  the  crucible,  and  poured  into  a 
small  cast-iron  mould,  warmed  and  slightly  oiled,  in  which 
it  forms  an  ingot  of  f  inch  in  width,  and  2  ozs.  in  weight. 
This  ingot  is  annealed  by  burying  it  in  hot  ashes,  and  ham 
mered  upon  a  steel  anvil  until  its  thickness  is  reduced  to 


Manufacture  of  Gold  L  eaf.  257 

^th  inch,  the  metal  being  once  or  twice  re-heated  or  annealed 
during  the  process.  The  gold  is  then  passed  between  per 
fectly  cylindrical  steel  rollers,  which  are  turned  at  exactly 
the  same  rate  in  opposite  directions,  until  it  is  reduced  to  a 
riband  so  thin  that  a  square  inch  of  it  weighs  6J  grains.  It 
is  of  course  necessary  to  anneal  the  gold  several  times 
during  the  rollings. 

The  riband  is  now  exactly  divided,  with  the  help  of  a  pair 
of  compasses,  and  cut  up  into  pieces  of  one  inch  square.  One 
hundred  and  fifty  of  these  pieces  are  piled  up  alternately 
with  pieces  of  tough  paper  or  vellum  (prepared  calf-skin) 
four  inches  square,  rubbed  over  with  a  little  fine  plaster  of 
Paris,  to  prevent  the  gold  from  sticking.  Twenty  vellums 
are  placed  above,  and  twenty  below  the  pile,  which  is  then 
firmly  secured  by  passing  two  strong  belts  of  parchment 
across  it. 

The  beating  is  performed  with  a  hammer  weighing  about 
1 6  Ibs.,  having  a  circular  face  four  inches  in  diameter  and 
somewhat  convex.  The  pile  is  placed  upon  a  heavy  block 
of  marble,  nine  inches  square,  sunk  into  a  very  strong  wooden 
bench.  The  workman  uses  the  hammer  with  one  hand, 
directing  the  blows  well  in  the  middle  of  the  pile,  and  turn 
ing  it  occasionally.  After  a  time,  the  packet  is  opened,  the 
middle  leaves  are  shifted  to  the  outside,  and  the  beating  is 
continued  until  the  leaves  have  been  extended  to  nearly  the 
same  size  as  the  vellums.  They  are  then  taken  out  of  the 
pile,  and  each  leaf  is  cut  with  a  sharp  knife  into  four  equal 
squares,  which  will  measure  about  an  inch  each  way.  These 
are  made  into  packets,  as  before,  with  gold-beaters'  skin,  a 
membrane  which  is  separated  from  the  outer  surface  of  the 
intestines  of  the  ox,  and  is  prepared  for  use  by  hammering 
it  between  folds  of  paper  in  order  to  extract  the  grease, 
and  steeping  it  in  an  infusion  of  nutmeg  and  cinnamon,  in 
order  to  preserve  it ;  it  is  then  dried  and  rubbed  over 
with  plaster  of  Paris.  The  packets  made  up  of  gold- 

s 


258      Metals  :  their  Properties  and  Treatment. 

beaters'  skin,  with  alternate  layers  of  gold,  are  beaten  as 
before,  but  with  a  ten-pound  hammer,  for  about  two  hours, 
the  packet  being  skilfully  rolled  and  bent  now  and  then,  in 
order  to  loosen  the  leaves.  When  these  are  again  extended 
to  about  4  inches  square,  they  are  spread  out  upon  a  leathern 
cushion,  and  cut  into  four  equal  squares  by  applying  a  cross  of 
cane  cut  to  sharp  edges,  and  fixed  upon  aboard.  These  squares 
are  again  made  up  into  packets  with  gold-beaters'  skin,  and 
hammered  put  a  third  time,  with  a  seven-pound  hammer,  to 
about  3^  inches  square.  They  are  then  dexterously  lifted 
off  the  skin,  with  a  delicate  pair  of  wooden  pincers,  spread 
out  upon  a  leathern  cushion  by  blowing  them  flat  down,  and 
cut  down  to  one  size  by  a  square  of  sharp-edged  cane  fixed 
to  a  board,  and  pressed  upon  the  leaf  of  gold  extended  on 
the  cushion.  The  gold  leaves  are  then  packed  between  the 
leaves  of  books  made  of  printed  paper,  rubbed  over  with  red 
chalk  to  prevent  adhesion  ;  there  are  usually  twenty-five 
leaves  in  each  book,  their  average  thickness  being  -sWuuijth 
of  an  inch.  Mechanical  power  has  been  lately  substituted 
for  manual  labour  in  gold-beating. 

When  one  of  these  leaves  is  held  up  to  the  light,  it  exhibits 
a  beautiful  green  colour,  and  if  it  be  rendered  still  thinner, 
either  by  beating,  or  by  floating  it  upon  a  very  weak  solution 
of  cyanide  of  potassium,  which  slowly  dissolves  it,  it  trans 
mits,  when  taken  upon  a  glass  plate  and  held  up  to  the  light, 
a  blue,  violet,  or  red  light,  in  proportion  as  its  thickness 
diminishes.  Even  when  it  is  so  transparent  that  one  may 
read  through  it,  the  yellow  colour  and  lustre  of  the  gold  are 
still  visible  by  reflected  light.  These  varying  colours  of 
finely-divided  gold  are  turned  to  account  in  the  colouring  of 
glass  and  in  painting  on  porcelain. 

Gold  Thread  is  made  by  covering  a  cylinder  of  silver  with 
gold  leaf,  and  drawing  it  through  a  wire-drawing  plate  until 
it  is  reduced  to  the  thinness  of  a  hair.  In  this  manner,  one 
grain  of  gold  is  made  to  cover  364  feet  of  wire.  For 
making  gold  lace,  this  wire  is  flattened  by  passing  it  between 


Gilding,  259 

rollers,  and  is  twisted  by  machinery  round  a  thread  of  yellow 
silk,  which  is  then  made  up  into  lace  or  braid. 

Gilding. — The  most  obvious  method  of  gilding  consists  in 
applying  gold  leaf  to  the  object  required  to  be  covered,  an 
art  requiring  great  delicacy  and  skill,  the  description  of 
which  does  not  fall  within  the  scope  of  this  work. 

Wash-Gilding  \$  effected  with  an  amalgam  of  gold,  prepared 
by  dissolving  one  part  of  fine  gold  in  eight  parts  of  mercury. 
The  gold  is  laminated,  placed  in  a  crucible,  heated  to  faint 
redness,  and  thrown  into  the  requisite  quantity  of  mercury, 
also  moderately  heated  in  a  crucible,  whilst  the  metals  are 
stirred  with  an  iron  rod  hooked  at  the  end.  When  all  the 
gold  is  dissolved,  the  amalgam  is  poured  into  water,  and 
squeezed  in  wash-leather  to  separate  the  excess  of  mercury. 
A  pasty  amalgam  is  thus  obtained,  containing  about  one- 
third  of  its  weight  of  gold. 

The  metals  generally  employed  for  wash-gilding  are 
brass,  and  copper  alloyed  with  one-seventh  of  brass,  nickel 
being  sometimes  added.  The  article  to  be  gilded,  after 
being  heated  to  redness  in  a  charcoal  or  peat  fire  and  cooled 
slowly,  is  dipped  in  very  dilute  sulphuric  acid,  rubbed 
with  a  hard  brush,  washed  and  dried.  It  is  then  dipped  in 
pretty  strong  nitric  acid  (sp.  gr.  1-33),  well  washed,  and 
dried  by  rubbing  with  bran.  By  this  treatment,  all  the  oxide 
has  been  removed  from  the  surface,  which  has  been  also 
sufficiently  corroded  or  roughened  by  the  acid  to  favour  the 
adhesion  of  the  amalgam  of  gold.  This  is  applied  to  the 
surface  with  a  brush  made  of  fine  brass  wire,  which  is  clipped 
into  a  solution  of  nitrate  of  mercury  made  by  dissolving  100 
parts  by  weight  of  mercury  in  no  parts  of  nitric  acid  (sp. 
gr.  1-33)  and  diluting  the  solution  with  25  times  its  weight 
of  water.  The  brush  being  wetted  in  this  solution,  which 
coats  it  with  a  thin  film  of  mercury  (p.  237),  is  rubbed  upon 
a  lump  of  the  amalgam,  which  is  then  brushed  over  the 
article  to  be  gilded ;  this  is  next  held  over  glowing  charcoal, 
and  well  turned  about,  until  it  is  hot  enough  to  make  a  drop 

s  2 


260       Metals :  their  Properties  and  Treatment. 

of  water  hiss,  when  the  whole  of  the  mercury  is  expelled  in 
the  form  of  vapour,  leaving  a  film  of  dead  gold  upon  the 
surface,  which  is  then  rubbed  with  a  wet  burnisher  of  haema 
tite.  Several  ourious  processes,  very  difficult  of  explanation, 
are  employed  by  persons  experienced  in  the  art  of  gilding, 
for  giving  the  required  shades  of  colour  and  degrees  of 
lustre  to  the  film  of  gold  left  by  the  mercury.  One  of  these, 
intended  to  produce  red  gold,  consists  in  coating  it  with 
gilders'  wax,  containing  wax,  red  ochre,  verdigris  (acetate  of 
copper)  and  alum.  The  object,  having  been  coated  with 
this  composition,  is  strongly  heated  in  the  flame  of  a  wood 
fire,  quenched  in  water,  and  scrubbed  with  vinegar.  This 
process  probably  reddens  the  gold  by  alloying  it  with  a  little 
copper  from  the  verdigris. 

Buttons,  trinkets,  &c.,made  of  brass  or  copper,  are  coated 
with  gold  by  immersing  them  in  a  boiling  alkaline  solution 
containing  that  metal.  2,400  grains  of  fine  gold  are  dissolved 
in  a  mixture  of  21  (avoirdupois)  ozs.  of  nitric  acid  (sp.  gr. 
1-45),  17  ozs.  of  hydrochloric  (muriatic)  acid  (sp.  gr.  i'i5), 
and  14  ozs.  of  distilled  water.  This  solution  of  (chloride  of) 
gold  is  mixed  with  4  gallons  of  distilled  water,  and  20  Ibs.  of 
bicarbonate  of  potash,  and  boiled  for  two  hours.  The  articles 
having  been  thoroughly  cleaned  from  oxide,  are  suspended 
from  a  hoop  of  brass  or  copper-wire,  and  moved  about  in  the 
boiling  liquid  until  they  are  judged  to  have  acquired  a  suf 
ficient  coating  of  gold,  which  is  the  case  after  less  than  a 
minute  with  small  articles.  The  gold  is  deposited,  in  this 
process,  in  consequence  of  the  copper  taking  its  place  in 
chemical  combination  in  the  liquid ;  the  film  is  bright  and 
not  dead  as  in  the  amalgamation  process,  but  it  may  be 
deadened,  if  required,  by  dipping  the  articles  in  solution  of 
nitrate  of  mercury  (p.  259)  before  exposure  to  the  gilding 
solution,  when  they  will  become  coated  with  mercury,  which 
will  form  an  amalgam  with  the  gold  deposited  from  the  solu 
tion,  and  this  will  be  left  as  a  dead  film  on  expelling  the 
mercury  by  heat. 


Mercury  or  Quicksilver.  261 

Electro-gilding'^  effected,  like  the  corresponding  process  of 
silvering  (p.  235),  by  immersing  the  thoroughly-cleansed 
articles  to  be  gilded  in  an  appropriate  solution  of  gold,  and 
connecting  them  by  metallic  wires  with  the  zinc  end  of  a 
galvanic  battery  of  which  the  copper  end  is  in  metallic  con 
nection  with  a  plate  of  gold,  which  is  gradually  dissolved, 
replacing  the  gold  which  has  been  deposited.  The  gilding 
bath  is  heated  by  steam  to  about  200°  F.,  which  facilitates 
the  deposition  of  the  metal.  A  solution  for  electro-gilding 
may  be  prepared  by  dissolving  1,550  grains  of  gold  in  a 
mixture  of  14  (avoirdupois)  ozs.  of  nitric  acid  (sp.  gr.  1*45), 
ii  ozs.  of  hydrochloric  acid  (sp.  gr.  1*15),  and  10  ozs.  of  water. 
To  this  liquid,  containing  the  chloride  of  gold,  a  solution  of 
cyanide  of  potassium  is  added  carefully,  as  long  as  any 
cyanide  of  gold  is  separated.  This  precipitate  is  allowed  to 
settle,  the  clear  liquid  drawn  off,  and  the  precipitate  redis- 
solved  in  some  more  solution  of  cyanide  of  potassium. 
Enough  water  is  then  added  to  bring  the  solution  up  to  five 
gallons. 

In  gilding  polished  iron  and  steel,  they  are  heated  until 
they  assume  a  blue  tint,  and  successive  coatings  of  gold  leaf 
are  applied  with  a  burnisher,  a  gentle  heat  being  employed 
after  every  coating  except  the  last,  which  is  burnished  cold. 


MERCURY. 

This  metal,  also  called  quicksilver •,  is  of  very  rare  occurrence 
in  Great  Britain,  the  whole  of  the  mercury  employed  in  the 
arts  being  imported  from  Austria,  Spain,  .California,  and 
China,  the  largest  quantity  of  the  metal  being  now  furnished 
by  California.  A  considerable  quantity  is  found  in  the 
metallic  state,  either  collected  in  cavities,  or  disseminated  in 


262       Metals :  their  Properties  and  Treatment. 

globules  throughout  its  ore  cinnabar*  which  has  the  same 
composition  as  vermilion*?  being  a  compound  of  mercury 
with  sulphur,  containing,  when  pure,  86  parts  of  mercury  in 
the  hundred.  Native  mercury  sometimes  contains  silver. 
Cinnabar  is  usually  met  with  in  moderately  hard  dark 
brown  masses  which  are  very  heavy  (sp.  gr.  8*2),  and  exhibit 
a  red  colour  when  scraped  with  a  knife.  Some  specimens 
have  a  red  colour  without  scraping,  and  all  yield  a  powder 
of  a  more  or  less  bright  red  colour. 

Native  calomel,  a  combination  of  mercury  with  chlorine,  is 
sometimes  found  in  very  small  quantity  associated  with  cin 
nabar. 

A  rich  deposit  of  cinnabar  is  reported  to  have  been  lately 
discovered  in  Borneo. 

The  extraction  of  mercury  from  its  ore  is  effected,  like  that 
of  zinc,  by  distillation,  but  since  this  metal  is  converted  into 
vapour  at  a  much  lower  temperature  than  zinc  (mercury  boils 
at  662°  F.),  it  requires  much  more  elaborate  arrangements 
for  the  condensation  of  its  vapour  into  the  liquid  form,  and 
in  many  works  a  considerable  quantity  of  the  metal  is  wasted, 
on  account  of  the  imperfect  character  of  the  condensers,  the 
escaping  vapour  proving  most  injurious  to  the  health  of  the 
persons  employed.  Indeed  the  metallurgy  of  mercury,  in 
all  its  branches,  is  lamentably  injurious  to  health,  the  miners 
as  well  as  the  smelters  being  liable  to  salivation,  and  seldom 
living  to  an  old  age. 

The  mines  at  Almaden,  a  town  of  La  Mancha,  in  Spain, 
have  been  the  most  productive,  the  cinnabar  being  found  in 
large  veins  surrounded  by  sandstone  and  clay  slate.  The 
mercury  is  extracted  by  simply  roasting  the  ore,  when  the 
oxygen  of  the  air  converts  the  sulphur  into  sulphurous  acid 
gas,  and  the  mercury  passes  off  in  vapour. 

*  Derived  immediately  from  the  Latin  cinnabaris,  applied  not  only 
to  this  ore,  but  apparently  also  to  red-lead,  and  to  the  red  gum-resin 
known  as  dragorfs  blood,  from  the  Indian  name  of  which,  cinoper,  the 
word  appears  to  have  originated. 

t  Probably  from  vermeil,  French  for  red  coral. 


Aludcl  Furnace. 


263 


264      Metals :  their  Properties  and  Treatment. 

The  roasting  furnace  consists  of  a  fire-place  in  which  a 
wood  fire  is  maintained,  the  flame  of  which  kindles  the  ore 
stacked  upon  an  arch  of  fire-brick  (c,  Fig.  94),  provided 
with  openings  for  the  passage  of  the  flame.  Upon  this  arch 
some  large  blocks  of  sandstone,  very  poor  in  cinnabar,  are 
piled;  above  these,  small  fragments  of  richer  ores,  over  which 
again  are  placed  the  cakes  made  up  by  kneading  with  clay  the 
finely-divided  mercury  which  has  condensed  from  the  fumes 
without  running  together  into  liquid  metal,  as  well  as  any 
cinnabar  which  has  escaped  in  vapour  unchanged  during  a 
previous  roasting,  and  has  been  condensed  again  as  a  black 


FIG.  95. — Plan  of  Aludel  Furnace  for  extraction  of  Mercury. 

powder.  The  air,  which  enters  through  the  openings  in  the 
brick  arch,  furnishes  oxygen  to  the  sulphur  of  the  sulphuret 
of  mercury,  and  converts  it  into  sulphurous  acid  gas,  while 
the  mercury  does  not  combine  with  oxygen,  but  separates  in 
the  metallic  state,  being  converted  into  vapour,  partly  by  the 
heat  of  the  fire  beneath,  partly  by  that  produced  in  the  com 
bustion  of  the  sulphur.  The  sulphurous  acid  gas  and  the 
vapour  of  mercury  pass  out  through  flues  (0,  Fig.  95)  in  the 
side  of  the  furnace,  into  the  condensing  apparatus,  which 
consists  of  300  pear-shaped  stoneware  pipes,  called  aludels 

(Fig.  96),  open  at  both  ends, 
and  fitted  into  each  other, 

FIG.  96.-Aiudeis.  the  Joints  being  cemented 

together  with  clay.     These 

are  arranged  so  as  to  form  twelve  separate  flues,  each  corn- 


Extraction  of  Mercury  at  Idria.  265 

posed  of  25  aludels,  The  first  12  of  each  set,  nearest  to 
the  furnace,  incline  downwards,  towards  a  central  gutter  (K), 
whilst  the  last  twelve  ascend  a  corresponding  inclined  plane, 
the  centre  aludel  of  the  series  being  perforated  in  the  lower 
side,  so  that  the  condensed  mercury  may  run  out  into  a 
gutter  which  conducts  it  into  receiving  basins  (m,  n,  Fig.  95) 
underneath  the  furnace.  The  vapour  of  mercury  which 
escapes  condensation  in  the  aludels  passes,  together  with  the 
sulphurous  acid  gas,  into  a  chamber  (i,  Fig.  94)  in  which  a 
further  considerable  quantity  of  the  mercury  is  condensed 
to  the  liquid  state.  The  sulphurous  acid  gas  eventually 
escapes  through  the  chimney. 

The  imperfect  character  of  this  condensing  apparatus  is 
evident;  the  loss  of  mercury  vapour  through  the  leakage  of 
the  .numerous  joints,  and  through  the  openings  in  the  lowest 
aludels,  must  be  very  great,  so  that  it  is  not  surprising  that 
only  10  parts  of  mercury  should  be  extracted  from  a  hundred 
parts  of  rich  ore.  Each  roasting  lasts  about  twelve  hours, 
and  the  furnace  requires  three  or  four  days  to  cool  before 
receiving  a  fresh  charge,  affording  a  striking  contrast  to  the 
system  of  nearly  continuous  working  adopted  in  the  metal- 
lurgic  processes  of  this  country. 

The  mercury  mines  at  Idria  in  Austria,  which  are  now 
probably  more  important  than  those  at  Almaden,  were 
formerly  worked  by  state  prisoners  and  criminals,  on  account 
of  the  unhealthy  nature  of  the  occupation.  In  these  mines 
the  ore  is  found  both  in  limestone  and  in  a  bituminous  slate, 
and  contains  a  considerable  proportion  of  bituminous  matter. 
Previously  to  the  year  1794,  the  aludel  furnace  just  described 
was  also  employed  at  Idria,  but  it  was  then  superseded  by  a 
very  large  brick  structure  containing  a  series  of  condensing 
chambers.  The  roasting  furnace  (Fig.  97)  consists  of  a  grate 
upon  which  wood  is  burnt,  surmounted  by  three  perforated 
arches  (n  p  r)  of  fire-brick,  for  receiving  the  ore,  the  large 
fragments  being  placed  upon  the  lowest  arch,  the  smaller 
pieces  on  the  next,  whilst  the  uppermost  supports  a  number 


266      Metals ':  tJicir  Properties  and  Treatment. 

of  shallow  earthen  dishes  (s)  containing  the  dust  of  the  ore 
and  the  mercurial  soot  from  former  operations.  Air  is  ad 
mitted  to  the  heated  ore  through  small  passages  in  the  walls, 


FIG.  97. — Extraction  of  Mercury  at  Idria.  G  H,  Passages  from  which  air 
enters  through  flues  into  the  space  occupied  by  the  ore.  c,  Condensing 
chambers. 

and  the  sulphurous  acid  and  vapour  of  mercury  are  drawn, 
by  the  two  chimneys,  through  six  condensing  chambers  (c  D, 
Fig.  98)  on  each  side  of  the  furnace,  so  connected  by  nar 
row  openings  that  the  vapours  are  forced  to  pervade  one 


FIG.  98. — Section  of  Idrian  Furnace  and  Condensing  Chambers.  A,  Fire 
place.  B,  Arches  upon  which  the  ore  is  placed.  CUE,  Condensing 
chambers.  G  H,  Air  channels. 

chamber  before  entering  another.  In  the  last  chamber  (D) 
of  each  series,  which  is  surmounted  by  the  chimney,  the  last 
portions  of  mercury  are  condensed  by  a  cascade  of  water.  The 


Extraction  of  Mercury  at  Idria.  267 

greater  portion  of  the  mercury  is  condensed  into  the  liquid  form 
in  the  first  three  chambers  of  each  series,  and  is  collected  in 
an  underground  gutter  which  conveys  it  into  a  tank,  from 
which  it  is  ladled  out  to  be  filtered  through  cloth,  and  put 
into  the  wrought-iron  bottles,  containing  about  60  Ibs.  each, 
in  which  it  is  imported  into  this  country.  The  three  last  of 
each  series  of  condensing-chambers  receive  the  remainder  of 
the  mercury  chiefly  in  the  form  of  dust  or  soot,  consisting  of 
finely-divided  mercury,  with  some  sulphuret  of  mercury 
which  has  escaped  in  vapour,  and  some  carbon  from  the 
bituminous  matter  in  the  ore.  About  a  week  is  required  to 
complete  the  distillation,  including  the  time  required  for 
cooling  the  furnace.  Only  about  8J-  parts  of  mercury  are 
obtained  from  100  parts  of  ore.  In  1803,  a  fire  broke  out 
in  the  mines  at  Idria,  and  the  combustion  was  sustained  by 
the  bituminous  matter  in  the  ore,  so  that  it  became  necessary 
to  flood  the  workings  with  water.  The  vapours  of  mer 
cury  evolved  proved  very  injurious  to  the  health  of  the 
neighbourhood. 

A  process  similar  to  that  employed  at  Idria  is  followed  at 
New  Almaden,  in  California,  for  the  extraction  of  the  mercury. 

Within  the  last  few  years,  a  greatly  improved  apparatus 
has  been  employed  at  Idria.  The  ore,  in  fragments  as  large 
as  a  fist,  is  thrown  through  a  hopper  into  a  deep  cylindrical 
fire-place,  upon  which  a  little  wood  and  coal  are  burnt. 
The  mercurial  vapours  are  conducted  into  six  condensing 
chambers  covered  with  iron  plates  and  kept  cool  by  a  stream 
of  water.  The  draught  through  the  chambers  is  maintained 
by  a  chimney,  where  terraces  are  constructed  over  which 
water  is  allowed  to  flow.  Fresh  charges  of  7  cwts.  of  ore 
and  28  Ibs.  of  charcoal  are  introduced  every  three-quarters 
of  an  hour,  and  the  spent  ore  is  raked  out  from  below 
through  the  moveable  bars  of  the  grate. 

A  still  more  scientifically  constructed  apparatus  is  em 
ployed  at  Idria  for  the  treatment  of  small  ores  containing 


268       Metals :  their  Properties  and  Treatment. 


one-hundredth  or  less  of  mercury,  in  which  the  ore  is  heated 
on  the  hearth  of  a  reverberatory  furnace  (a,  Fig.  99),  the 
mercurial  vapour  being  passed — i,  through  a  condensing 
chamber  (d) ;  2,  through  a  wide  sloping  iron  pipe  (/)  kept 
cool  by  the  constant  trickling  of  water  over  it,  from  the 
perforated  gutter  (e) ;  3,  into  a  second  condensing  chamber 
(g) ;  4,  through  a  second  iron  pipe  (h\  similar  to  the  first, 
into  a  chimney  (k).  The  hearth  of  the  reverberatory  furnace 
is  divided  into  three  compartments,  the  ore  being  first 


S  ,, — ^  J 


FIG.  99. — Modern  Idrian  Mercury-furnace. 

thrown,  through  a  hopper  (b\  upon  that  farthest  from  the 
grate,  being  raked  out  into  each  of  the  other  compartments 
in  succession,  so  as  to  be  exposed  to  a  gradually  increasing 
temperature  until  it  is  drawn  out  in  a  spent  condition 
through  a  channel  near  the  fire-bridge,  whilst  fresh  ore  is 
charged  at  the  other  end  of  the  hearth.  Wood  is  the  fuel 
employed.  Beside  the  liquid  mercury  which  is  run  out  into 
proper  receptacles,  a  large  proportion  of  mercurial  soot, 
containing  finely-divided  mercury,  is  collected  in  the  con 
densing  pipes  and  chambers.  This  is  dried,  raked  over  on 


Distillation  of  Cinnabar  with  Lime.  269 


an  inclined  plane  as  long  as  any  mercury  runs  out,  and 
afterwards  distilled  to  obtain  the  last  portions  of  the  metal. 

On  the  west  bank  of  the  Rhine  there  are  several  small 
mercury  mines  which  yield  sulphuret  of  mercury  associated 
with  sandstone.  These  ores  are  made  to  yield  their  mercury 
by  distilling  them  with  lime,  a  process  generally  resorted  to 
in  the  smaller  mercury  works.  The  distillation  is  effected 
in  cast-iron  pear-shaped  vessels  (A,  Fig.  100),  thirty  of  which 
are  heated  by  the  same  fire,  in  a  gallery  furnace  (M),  the  grate 
of  which  runs  through  its  entire  length,  and  is  fed  with  coal, 
which  does  not  come 
into  contact  with  the 
iron  vessels,  these  being 
arranged  in  the  upper 
part  of  the  furnace,  on 
each  side  of  the  grate, 
in  two  rows,  one  above 
the  other,  so  that  the 
flame  may  circulate 
around  them  before 
escaping  through  the 
openings  into  the  chim 
ney.  The  ground  ore 
is  mixed  with  about 
one-fourth  of  its  weight 

of  quicklime,  and  about  yolbs.  of  the  mixture  are  intro 
duced  into  each  of  the  cast-iron  bottles,  which  are  then 
about  two-thirds  full.  The  neck  of  each  bottle  fits  into  a 
stone  bottle  (B)  half  full  of  water,  placed  outside  the  fur 
nace,  to  receive  the  mercury.  The  water  above  the  metal 
becomes  filled  with  black  mercury  containing  undecomposed 
sulphuret  and  finely-divided  mercury ;  this  is  dried  and 
distilled  again  with  more  lime. 

In  this  process,  the  lime,  or  oxide  of  calcium,  composed 
of  calcium  and  oxygen,  decomposes  with  the  sulphuret  of 
mercury,  yielding  sulphuret  of  calcium,  which  remains  in  the 


FIG.  100. — Extraction  of  Mercury  in  the 
Palatinate. 


270       Metals :  their  Properties  and  Treatment. 


iron  bottle,  mercury  which  passes  over  in  vapour,  and  oxygen 
which  converts  a  part  of  the  sulphuret  of  calcium  into 
sulphate  of  lime. 

This  operation  in  the  gallery  furnace  is  obviously  attended 
with  waste  and  inconvenience.  The  trouble  of  charging 
and  discharging  so  many  small  bottles  and  of  cementing  the 
joints  is  very  considerable,  and  has  led  to  the  introduction, 
in  some  places,  of  another  arrangement  which  allows  the 
mercury  to  be  extracted  on  the  same  principle  but  with 
much  greater  economy. 

In  place  of  the  bot 
tles,  cast-iron  retorts 
(a,  Fig.  10 1 )  are  em 
ployed,  resembling 
those  used  in  distilling 
coal  for  gas.  These 
are  about  seven  feet 
long  and  one  foot 
square,  in  sectional 
area,  so  that  they  may 
be  charged  with  700 Ibs. 
(instead  of  70)  of  the 
mixture  of  the  ground 
cinnabar  with  lime,  in 
troduced  at  the  back 
of  the  retort,  which  LJ 
then  closed  with  an  iron  plate.  The  front  end  is  also  closed 
with  an  iron  plate  (a,  Fig.  102),  which  is  provided  with  a 
sloping  cast-iron  pipe  (^),  4  inches  in  diameter,  having  a  door 
through  which  it  may  be  cleared  with  a  wire.  This  pipe 
dips  into  water  contained  in  a  condenser  (c)  resembling  tlw 
hydraulic  main  of  the  gas  works,  being  an  iron  pipe,  1 8  inches 
wide,  and  20  feet  long,  which  runs  along  the  front  of  the  range 
of  nine  retorts,  and  receives  the  mercury  condensed  from  them, 
being  itself  kept  cool  by  a  stream  of  water  running  through  a 
wooden  trough  around  it.  This  pipe  is  a  little  inclined 


FIG.  lor. — Ure's  Retort  for  extraction  of 
Mercury  from  Cinnabar. 


Extraction  of  Mercury  from  Grey  Copper  Ore.     271 

towards  one  end,  so  that  the  condensed  mercury  may  run 
down  into  a  pipe  (D)  which  conveys  it  into  a  locked  cistern 
(<?)  (to  prevent  pilfering),  in  which  an  iron  float  (k)  indicates 
the  level  of  the  mercury.  The  end  of  the  pipe  in  the  cistern 
is  made  to  open  into  a  small  vessel,  which  is  filled  with  mer 
cury  at  the  commencement  to  prevent  the  water  from  running 
out  of  the  condenser.  The  latter  is  provided  with  a  safety 
valve  (g)  to  allow  for  any  sudden  expansion  or  contraction  of 
the  air  within.  The  retorts  are  set  like  gas  retorts,  so  that 
the  same  coal  fire  (i)  may  heat  three  of  them,  the  range  of 
nine  having  thrse  furnaces  with  flues  running  into  one 
chimney. 


FIG.  102. — lire's  Retorts  for  extraction  of  Mercury. 

In  Hungary,  a  considerable  quantity  of  mercury  is  ex 
tracted  from  the  grey  copper  ore  (Fahl-erz  vt  fallow  ore] 
during  the  process  of  roasting  preliminary  to  the  smelting  for 
copper.  The  roasting  is  effected  by  burning  the  ore  in 
mounds  about  40  feet  by  20,  and  4^  feet  high,  in  which 
channels  are  constructed  for  the  admission  of  a  moderate 
supply  of  air.  A  layer  of  small  ore  having  been  spread  upon 
the  ground,  and  covered  with  some  larger  pieces  of  ore 
already  once  roasted,  some  wood  and  coal  are  spread  over 
them,  then  a  layer  of  ore,  the  outside  being  covered  with 
powdered  ore  so  as  to  prevent  a  too  free  passage  of  air,  and 
to  retain  the  vapour  of  mercury.  The  heap  is  kindled  through 
shafts  left  for  the  purpose,  when  the  heat  evolved  by  the 


272       Metals:  their  Properties  and  Treatment. 

combustion  of  the  wood  and  coal  ignites  the  sulphur  of  the 
ore,  which  burns  away  as  sulphurous  acid,  whilst  the  mercury 
is  converted  into  vapour  and  condensed  among  the  cooler 
portions  of  the  fine  ore  on  the  outside  of  the  heap.  After 
about  three  weeks,  the  upper  layers  are  thrown  upon  a  sieve 
and  washed  with  water,  the  fine  ore  which  passes  through 
the  sieve  being  separated  from  the  mercury  by  washing. 

The  mercury  imported  into  this  country  generally  contains 
lead,  bismuth,  and  zinc  as  impurities,  which  cause  globules  of 
it  to  tail  or  leave  a  metallic  streak  behind  them  when  rolled 
over  a  glass  plate,  whilst  pure  mercury  runs  off  in  globules, 
leaving  the  glass  clean. 

It  is  sometimes  purified  by  re-distilling  it,  using  as  a  retort 
one  of  the  iron  bottles  in  which  it  is  imported ;  but  the  metal 
is  liable  to  violent  concussions  during  the  ebullition,  so  that 
it  is  impossible  to  prevent  a  part  of  the  impure  mercury  from 
splashing  over  into  the  receiver.  A  far  better  process  for 
purifying  it  consists  in  pouring  the  mercury  into  a  wide  dish 
(such  as  a  photographic  tray),  where  it  may  form  a  thin  layer, 
and  covering  its  surface  with  diluted  nitric  acid  (sp.  gr.  1*15). 
The  acid  is  allowed  to  remain  in  contact  with  it  for  a  day 
or  two,  being  frequently  stirred,  until  the  mercury  no  longer 
tails  upon  glass.  The  lead,  bismuth,  and  zinc  are  dissolved 
by  the  acid,  in  the  form  of  nitrates,  together  with  a  portion  of 
the  mercury,  so  that  the  acid  should  be  preserved  in  order 
to  assist  in  the  purification  of  another  portion  of  the  metal. 
The  mercury  may  be  separated  from  the  acid  by  pouring 
them  both  into  a  funnel  stopped  with  the  finger,  on  removing 
which  the  mercury  runs  off,  the  finger  being  replaced  to 
retain  the  acid ;  the  mercury  is  then  well  washed  with  water 
in  a  dish,  and  dried,  first  with  blotting-paper,  and  after 
wards  at  a  gentle  heat.  Any  dust  or  other  mechanical 
impurities  may  be  easily  removed  by  filtering  the  mercury 
through  a  cone  of  writing-paper,  in  the  apex  of  which  a 
few  pin-holes  have  been  made. 

An  old  and  simple  process  for  the  purification  of  a  small 


Uses  of  Mercury.  273 

quantity  of  mercury,  consists  in  shaking  it  in  a  bottle  with 
air  and  a  little  powdered  sugar,  which  helps  to  divide  the 
mercury  and  expose  the  lead,  &c.,  to  the  action  of  the  air, 
which  converts  them  into  a  grey  powder.  By  repeating  the 
agitation  with  fresh  portions  of  air,  nearly  all  the  foreign 
metals  may  be  removed,  and  the  sugar  with  the  adhering 
oxides  may  be  separated  by  filtering  through  pricked  paper. 

Many  of  the  useful  applications  of  mercury  depend  upon 
its  being  the  heaviest  substance  which  is  liquid  at  the  ordi 
nary  temperature.  Its  specific  gravity  being  13.54,  a  column 
of  mercury  thirty  inches  high  serves,  in  the  barometer,  to 
measure  the  pressure  of  the  atmosphere,  whilst  thirty- three 
feet  (396  inches)  of  water  are  required  for  the  same  purpose. 

The  great  interval  between  the  temperature  at  which  mer 
cury  congeals  to  the  solid  state  (71  degrees  below  the  freez 
ing  point  of  water)  and  that  at  which  it  boils  (450  degrees 
above  the  boiling-point  of  water)  renders  it  especially  suit 
able  for  filling  thermometers,  an  application  for  which  it  is 
also  recommended  by  the  circumstance  that  it  has  a  very 
low  specific  heat,  or  requires  much  less  heat  to  raise  it  to  a 
given  temperature  than  most  other  liquids  which  could  be 
employed  for  thermometric  purposes  :  thus,  a  spirit  thermo 
meter,  in  which  alcohol  is  used  to  show  the  expansion,  rises 
and  falls  much  more  slowly  than  the  mercurial  thermometer, 
because  the  specific  heat  of  alcohol  is  15  times  as  great  as 
that  of  mercury  ;  in  other  words,  fifteen  seconds  would  be 
required  by  a  spirit-thermometer  to  measure  a  temperature 
which  would  be  indicated  in  one  second  by  a  mercurial  ther 
mometer  of  the  same  weight.  A  further  advantage  on  the 
side  of  mercury  is  derived  from  its  not  adhering  to  the  glass. 
Moreover,  in  a  spirit-thermometer,  the  indications  are  affected 
by  the  presence  of  the  vapour  of  alcohol  in  the  space  above 
the  column,  which  should  be  perfectly  vacuous,  and  is  nearly 
so  in  the  case  of  the  mercurial  thermometer,  for  the  metal 
does  not  evolve  an  appreciable  amount  of  vapour  at 
temperatures  below  the  boiling-point  of  water. 

T 


274       Metals :  their  Properties  and  Treatment. 

That  mercury  does  give  off  a  minute  quantity  of  vapour, 
even  at  the  ordinary  temperature,  is  shown  by  the  appear 
ance  of  minute  globules  of  metal  condensed,  in  cold  weather, 
upon  the  glass  in  the  upper  part  of  a  barometer,  and  by  the 
experiment  of  suspending  a  gold  leaf  at  an  inch  or  two  above 
the  surface  of  mercury  in  a  bottle,  when  it  is  found,  after 
some  time,  to  be  whitened  by  the  combination  of  mercury 
vapour  with  the  gold. 

Mercury  is  remarkable  for  its  properly  of  uniting  with 
other  metals  at  the  ordinary  temperature,  to  form  combina 
tions  which  are  termed  amalgams.  Iron  and  platinum  are 
the  only  metals  in  ordinary  use  which  are  not  attacked  by 
mercury.  It  adheres  to  platinum  and  wets  its  surface,  but 
does  not  unite  chemically  with  it.  Gold  is  soon  penetrated 
by  mercury,  and  becomes  very  brittle.  The  surface  of  a 
gold  ring,  for  instance,  is  instantly  whitened  by  mercury, 
and  if  allowed  to  remain  in  contact  with  it  for  a  short  time, 
the  gold  is  rendered  so  brittle  as  to  be  useless ;  a  mere  ex 
ternal  coating  of  amalgam  may  be  removed,  and  the  colour 
of  the  gold  restored,  by  warming  it  with  a  little  nitric  acid, 
the  surface  of  the  gold  being  afterwards  burnished. 

Silvering  Looking-glasses. — An  amalgam  of  tin  is  employed 
for  silvering  the  backs  of  looking-glasses,  which  is  performed 
in  the  following  manner.  A  sheet  of  tin-foil  (generally  har 
dened  by  a  minute  proportion  of  copper),  somewhat  larger 
than  the  plate  to  be  silvered,  is  laid  upon  a  stone  or  marble 
table,  which  is  swung  upon  an  axis  so  that  it  may  be 
gradually  sloped  by  a  screw  when  required.  The  upper 
surface  of  this  table  is  perfectly  smooth  and  level,  and  has 
a  gutter  running  round  it,  with  a  spout  for  collecting  the 
superfluous  mercury.  The  tin-foil  is  applied  to  the  table 
with  a  brush,  so  that  it  may  be  free  from  wrinkles,  and  the 
surface  having  been  laid  truly  horizontal,  a  little  mercury 
is  spread  over  it  with  a  roll  of  flannel,  so  that  every  part  of 
the  tin-foil  may  be  amalgamated.  A  very  thin  layer  of 
mercury  is  then  poured  over  the  surface,  and  the  edge  of  the 


Amalgams.  275 

clean  dry  plate  to  be  silvered  is  very  carefully  pushed  for 
ward  over  the  table,  so  as  to  carry  the  superfluous  mercury 
before  it,  and  to  prevent  any  air  from  entering  between  the 
amalgam  and  the  glass.  Some  flannel  is  placed  on  the 
glass,  with  a  weight  upon  it,  and  the  table  is  very  slightly 
inclined  to  drain  off  the  excess  of  mercury.  After  about  five 
minutes,  the  plate  is  loaded  with  several  heavy  weights,  and 
allowed  to  remain  for  twenty-four  hours,  in  order  that  the 
amalgam  may  be  made  to  adhere  firmly  to  the  glass ;  the 
inclination  of  the  table  is  somewhat  increased  from  time  to 
time,  to  promote  the  draining  away  of  the  excess  of  mercury. 
When  the  weights  are  removed,  the  plate  is  laid  upon  a 
sloping  wooden  table,  the  upper  edge  of  which  is  raised 
gradually  by  a  pulley  until  the  plate  is  perpendicular. 
After  three  or  four  weeks,  when  the  excess  of  mercury  has 
drained  off,  the  looking-glass  is  ready  for  framing.  The 
amalgam  adhering  to  the  glass  contains  one  part  of  mercury 
and  four  parts  of  tin. 

The  amalgam  which  is  employed  to  promote  the  action  of 
glass  electrical  machines  is  composed  of  two  parts  of  zinc  and 
five  parts  of  mercury. 

Magnetic  amalgam  is  the  somewhat  fanciful  name  bestowed 
upon  the  amalgam  of  one  part  of  metallic  sodium  with  thirty 
parts  of  mercury,  which  is  liquid  at  a  very  moderate  heat,  but 
solidifies  on  cooling  to  a  hard  crystalline  mass.  It  is  cast  into 
ingots  which  are  kept  in  air-tight  iron  vessels  with  lime,  to 
absorb  any  moisture,  which  would  act  upon  the  sodium  in 
the  amalgam  and  convert  it  into  soda.  This  amalgam  is 
exported  to  the  amalgamating  mills  for  gold  and  silver 
ores,  where  it  encourages  the  amalgamation  and  prevents 
flouring  (p.  221). 

An  amalgam  of  one  part  of  cadmium  and  three  parts  of 
mercury  is  employed  by  dentists. 


T  2 


276      Metals :  their  Properties  and  Treatment. 


PLATINUM. 

This  valuable  metal  has  been  brought  into  use  in  quite 
modern  times,  having  been  discovered  by  an  assayer  in 
Jamaica  in  1741,  becoming  generally  known  in  Europe  in 
1 748.  Its  name,  derived  from  the  Spanish,  signifies  little  silver, 
since  it  somewhat  resembles  that  metal  in  colour;  it  has  also 
been  called  white  gold,  and  it  is  said  that  when  first  discovered, 
much  of  it  was  thrown  away,  lest,  from  its  durability  and  high 
specific  gravity,  it  should  be  employed  for  debasing  gold,  an 
expectation  which  has  been  partly  realised  (p.  253). 

Platinum  always  occurs,  like  gold,  in  the  metallic  state, 
and  most  commonly  in  alluvial  deposits  in  which  gold  is 
also  present.  Nuggets  of  platinum  have  rarely  been  found, 
the  large-st  on  record  being  one  of  18  Ibs.  weight.  The 
metal  is  commonly  met  with  in  flattened  grains  of  a  light 
steel-grey  colour.  The  Ural  mountains  have  furnished  the 
largest  quantity  of  platinum,  but  it  has  also  been  obtained 
from  Brazil,  Peru,  Borneo,  Australia  and  California. 

The  Platinum  ore,  as  it  is  called,  is  separated  from  the 
earthy  matters  by  washing  the  latter  away,  when  the  grains 
of  platinum  remain  behind  with  grains  of  gold,  magnetic  iron 
ore,  corundum,  and  a  very  heavy  alloy  of  osmium  and 
iridium.  The  platinum  itself  is  far  from  pure,  containing 
only  from  75  to  85  parts  of  that  metal  in  a  hundred,  the 
remainder  consisting  of  iron,  sometimes  found  to  the  amount 
of  13  per  cent,  iridium,  rhodium,  palladium,  osmium,  and 
copper.  When  any  considerable  quantity  of  gold  dust  is 
present,  it  is  separated  from  the  platinum  by  the  process  of 
amalgamation.  The  magnetic  iron  ore  is  extracted  by  a 
magnet. 

The  original  process  for  extracting  platinum  from  the  ore 
is  rather  a  chemical  than  a  metallurgical  operation,  but  since 


Extraction  of  Platinum.  277 

it  was,  until  within  the  last  few  years,  the  only  method  by 
which  the  metal  was  produced  in  a  marketable  state,  a  short 
description  of  it  is  here  given. 

The  grains  of  platinum  ore  are  heated  with  nitric  acid, 
which  dissolves  any  silver,  copper,  iron,  and  lead,  in  the  form 
of  nitrates ;  after  these  have  been  extracted,  the  residue  is 
washed  with  water,  and  heated  with  hydrochloric  acid,  which 
dissolves  the  magnetic  oxide  of  iron  ;  it  is  then  again  washed 
with  water,  and  gently  heated  for  several  hours  with  hydro 
chloric  acid  to  which  a  little  nitric  acid  is  added  from  time 
to  time.  The  platinum  is  thus  dissolved,  together  with  pal 
ladium,  rhodium,  and  some  iridium,  whilst  the  osmium  and 
the  rest  of  the  iridium  are  left  undissolved.  The  acid  solu 
tion  containing  the  chlorides  of  platinum,  &c.,  is  poured  off, 
and  the  residue  heated  with  fresh  portions  of  acid  as  long  as 
anything  is  dissolved,  when  any  quartz  and  corundum  are 
left,  together  with  the  grains  of  the  alloy  of  osmium  and 
iridium,  which  are  employed,  on  account  of  their  surpassing 
all  other  metallic  substances  in  hardness,  for  making  the 
nibs  of  gold  pens  upon  the  points  of  which  they  are  soldered. 

The  liquid  containing  the  chloride  of  platinum  is  mixed 
with  a  solution  of  sal-ammoniac  (muriate  of  ammonia)  con 
taining  one-sixth  of  its  weight  of  the  salt,  of  which  about  four 
parts  are  employed  for  every  ten  parts  of  the  ore.  A  yellow 
precipitate  is  then  deposited,  which  contains  the  greater 
part  of  the  platinum,  in  the  form  of  ammonio-chloride  of 
platinum,  a  combination  of  sal-ammoniac  with  chloride  of 
platinum. 

This  yellow  precipitate  is  washed  with  cold  water,  dried, 
and  strongly  heated  in  a  plumbago  crucible,  when  the  sal- 
ammoniac  and  the  chlorine  are  driven  off,  and  spongy  plati 
num  is  left  as  a  grey  porous  mass.  This  is-  finely  powdered 
in  a  wooden  mortar,  rubbed  to  a  paste  with  water,  passed 
through  a  sieve  in  order  to  render  it  perfectly  uniform,  and 
poured  into  a  slightly  conical  brass  mould  closed  below  with 
blotting-paper  wrapped  round  a  steel  stopper.  When  the 

T  3 


278       Metals :  their  Properties  and  Treatment. 

water  has  drained  off,  a  plunger  is  forced  in  by  a  coining 
press,  so  as  to  condense  the  mass,  which  has  at  first  the 
specific  gravity  4-3,  until  its  specific  gravity  is  10,  when  it  has 
been  reduced  to  about  two-fifths  of  its  former  bulk,  and  has 
acquired  a  metallic  appearance.  The  disk  is  now  sufficiently 
coherent  to  be  removed  from  the  mould  and  intensely  heated 

for  about  36  hours  in  a 
porcelain  kiln,  when  it 
contracts  to  about  four- 
fifths  of  its  former  vol 
ume.  It  is  taken  out  of  the 
furnace  at  a  white  heat, 
and.  hammered  upon  its 
ends,  not  upon  the  sides, 
lest  it  should  crack. 
After  being  heated  and 
hammered  in  this  way 
several  times,  the  par 
ticles  become  thoroughly 
welded'  together  into  a 
compact  malleable  mass 
of  metal,  of  specific 
gravity  21-5. 

Instead  of  welding  the 
platinum  into  a  compact 
mass,  it  is  now  some 
times  melted  in  a  cru 
cible  by  the  intense  heat 
of  the  oxy-hydrogen 
blowpipe-flame.  The 


Fig.  103. — Platinum  melted  in  Crucible  by  the 
Oxy-hydrogen  Blowpipe. 

crucible  is  made  of  gas-carbon,  and  is  enclosed  in  another 
crucible  (i,  Fig.  103)  made  of  lime,  and  provided  with  a  conical 
cover  (G)  of  the  same  material.  The  furnace  is  made  of  three 
blocks  of  lime  strengthened  by  iron  wire,  one  (D)  serving 
for  the  hearth,  upon  which  is  placed  a  hollow  cylinder  (B)  of 
lime,  which  has  been  bored  in  the  lathe  until  it  is  wide 


Extraction  of  Platinum.  279 

enough  to  leave  a  clear  space  (H)  of  about  Jth  inch  round 
the  lime  crucible.  At  the  lower  part  of  this  cylinder  are 
four  openings  (K)  for  the  escape  of  the  steam  produced  in 
the  combustion  of  the  hydrogen  and  oxygen.  The  furnace 
is  covered  in  with  a  block  of  lime  (A)  about  2\  inches  thick, 
in  which  a  slightly  conical  passage  is  bored  for  the  reception 
of  the  blowpipe-jet  which  passes  down  to  within  an  inch  of 
the  apex  of  the  conical  cover  of  the  lime  crucible.  The 
blowpipe  (E)  consists  of  two  concentric  copper  tubes,  the 
outer  one  through  which  the  hydrogen  is  passed  being  about 
-L  inch  in  diameter,  and  terminating  in  a  somewhat  tapering 
nozzle  of  platinum  (c)  about  4  inch  long,  which  fits  into 
the  conical  passage  through  the  upper  block  of  lime.  The 
oxygen  is  conveyed  through  the  inner  copper  tube,  also 
furnished  with  a  platinum  nozzle,  the  opening  of  which  is 
about  -j^th  inch  in  diameter. 

The  hydrogen  and  oxygen  are  supplied  from  their  respec 
tive  gas-holders,  their  passage  being  regulated  by  the  stop 
cocks  H  o,  under  a  pressure  of  about  16  inches  of  water,  the 
hydrogen  being  lighted  before  the  oxygen  is  turned  on. 

The  new  process  for  extracting  platinum  from  its  ores 
resembles  one  of  the  methods  of  extracting  gold  and  silver, 
the  metal  being  dissolved  out  by  melted  lead  and  afterwards 
recovered  by  cupellation. 

Two  hundredweight  of  the  platinum  ore  mixed  with  an 
equal  weight  of  galena  (sulphuret  of  lead)  is  thrown,  in  small 
portions,  into  the  concave  hearth  of  a  small  reverberatory  fur 
nace  built  of  fire-brick.  The  materials  are  stirred  with  an  iron 
rod  until  the  platinum  has  entirely  dissolved  in  the  fused  galena. 
A  little  glass  is  then  introduced,  to  melt  over  the  surface,  and 
a  quantity  of  litharge  (oxide  of  lead)  equal  in  weight  to  the 
galena  is  gradually  added.  The  sulphur  in  the  sulphuret 
combines  with  the  oxygen  of  the  oxide,  and  passes  off  as 
sulphurous  acid  gas,  leaving  the  metallic  lead  in  combination 
with  the  platinum,  whilst  the  alloy  of  osmium  and  iridium, 
being  unaffected  by  the  lead,  sinks,  in  separate  grains,  to  the 


2 So       Metals:  their  Properties  and  Treatment. 

bottom  (its  specific  gravity  varying,  according  to  its  com 
position,  from  19-4  to  21-1).  After  remaining  at  rest  for 
some  time,  the  upper  portions  are  ladled  out  and  cast  into 
ingots,  and  the  remainder  is  added  to  the  next  charge. 

The  lead  containing  platinum  is  treated  in  a  cupellation 
furnace  (p.  208),  when  the  lead  is  removed  as  an  oxide. 


INS. 


FIG.  104. — Lime  Furnace  for  melting  Platinum  with  the  Oxy-hydrogen  Blow- 

S'pe.     a  a,   Blocks  of   lime    hollowed   out  to   form    the   furnace,     k  k, 
penings  for  the  oxy-hydrogen  blowpipes,     e  c,  Outer  tubes  conveying 
the  hydrogen  or  coal-gas,      h  h,    Inner  tubes  conveying   the   oxygen. 
d,  Spout  for  pouring  the  melted  platinum. 

leaving  the  platinum  in  a  spongy  state  upon  the  cupel, 
whence  it  is  transferred  to  a  small  furnace  made  of  lime 
(Fig.  104)  and  melted  by  the  flame  of  the  oxy-hydrogen 
blowpipe  (in  which  coal-gas  may  be  substituted  for  hydrogen), 
the  intense  heat  of  which  volatilises  any  silver,  gold,  lead, 
palladium  and  osmium.  When  the  metal  is  sufficiently 


Uses  of  Platinum.  281 

refined,  it  is  poured  through  an  opening  in  the  side  of  the 
furnace  into  an  ingot  mould  made  of  gas-carbon  or  of 
wrought  iron  lined  with  platinum.  In  this  manner,  25  Ibs. 
of  platinum  have  been  melted  and  refined  in  three-quarters 
of  an  hour,  with  a  consumption  of  about  43  cubic  feet  of 
oxygen.  The  melted  platinum  resembles  silver  in  its  pro 
perty  of  absorbing  oxygen  mechanically  at  a  high  tem 
perature  and  evolving  it  again  as  it  cools,  exhibiting  the 
phenomenon  of  sprouting  (p.  211). 

Since  platinum  is  one  of  the  most  malleable  and  ductile 
of  the  metals,  being  surpassed,  in  the  former  quality,  only  by 
gold,  silver  and  copper,  and  in  the  latter  by  gold  and  silver, 
it  is  easily  rolled  into  sheets  or  drawn  into  wire. 

The  principal  uses  of  platinum  depend  upon  its  resistance 
to  the  action  of  heat,  of  oxygen,  and  of  acids.  The  largest 
quantity  of  the  metal  is  devoted  to  the  manufacture  of  the 
stills  employed  for  boiling  down  oil  of  vitriol  in  order  to 
expel  the  water,  and  of  the  siphons  used  for  drawing  the  hot 
acid  out  of  the  stills.  Similar  stills  are  also  employed  in  the 
operation  of  parting  gold  and  silver  with  sulphuric  acid 
(p.  247).  The  joints  of  these  stills  are  soldered  with  fine 
gold,  and  they  are  usually  gilded  inside,  for  otherwise  they 
are  liable  to  become  porous  under  the  influence  of  the 
boiling  acid,  allowing  it  to  exude.  They  are  protected  from 
external  injury  and  from  the  direct  action  of  the  fuel  by  an 
iron  casing.  Some  platinum  stills  have  been  made  weighing 
upwards  of  60  Ibs.  and  costing  above  2,ooo/.  They  are 
slowly  corroded  by  the  action  of  the  acid,  and  require  occa 
sional  repair  by  soldering  them  with  gold. 

Platinum  is  also  much  employed  for  evaporating  basins 
and  crucibles  for  chemical  purposes,  and  thin  foil  and  wire  of 
this  metal  are  indispensable  in  operations  with  the  blowpipe. 
When  the  particles  of  the  metal  have  been  imperfectly 
consolidated  by  hammering,  it  is  found  to  blister  under  the 
influence  of  a  very  high  temperature.  The  permanence  of 
platinum  under  the  action  of  heat  has  led  some  persons  to 


282       Metals:  tlirir  Properties  and  Treatment. 

adopt  an  erroneous  estimate  of  its  durability  under  other 
conditions,  so  that  it  is  often  forgotten  that  platinum  is  a 
soft  metal  and  therefore  ill-adapted  to  resist  ordinary  wear. 
It  is  easily  corroded  and  rendered  brittle  by  carbon  and 
silica,  both  of  which  are  present  in  coal,  coke,  and  charcoal, 
for  which  reason  platinum  crucibles  are  never  allowed  to 
come  into  direct  contact  with  the  solid  fuel,  but  are  heated 
either  in  the  flame  of  a  gas  or  spirit  lamp,  or  in  a  muffle 
(p.  255),  or  enclosed  in  a  clay  crucible  lined  with  magnesia 
to  prevent  the  platinum  from  sticking  to  the  heated  clay. 

Metals  must  never  be  melted  in  platinum  crucibles,  since 
most  of  the  metals  are  capable  of  forming  alloys  with  it. 
Caustic  alkalies  and  saltpetre  in  a  melted  state  also  act  upon 
the  metal,  and  phosphorus  and  arsenic  combine  with  and 
corrode  it  very  rapidly  at  moderately  high  temperatures. 

Neither  sulphuric,  hydrochloric,  nitric  or  hydrofluoric  acid 
separately  has  any  action  upon  platinum,  but  a  mixture  of 
hydrochloric  with  nitric  acid  dissolves  it,  though  more  slowly 
than  it  dissolves  gold. 

An  alloy  of  platinum,  indium  and  rhodium  is  sometimes 
employed  for  crucibles,  which  are  harder  and  less  easily 
corroded  than  those  made  of  pure  platinum.  To  obtain  the 
alloy,  the  ore  of  platinum  (which  contains  the  two  other 
metals)  is  mixed  with  a  quantity  of  lime  equal  to  that  of  the 
iron  contained  in  the  ore,  and  fused  by  the  oxy-hydrogen 
blowpipe  in  a  furnace  made  of  lime  (p.  280).  The  iron 
and  copper  are  converted  into  oxides  which  form  a  fusible 
slag  with  the  lime,  whilst  the  gold,  palladium  and  osmium 
are  expelled  in  the  form  of  vapour,  and  the  alloy  of  platinum, 
iridium  and  rhodium  remains. 

Small  tubes,  &c.,  may  be  easily  extemporised  with  platinum 
wire  and  foil,  by  taking  advantage  of  the  readiness  with 
which  surfaces  of  this  metal  unite  when  hammered  at  a  high 
temperature. 

Platinum  vessels  are  cleaned  by  smearing  them  with  a 
paste  containing  equal  bulks  of  borax  and  cream  of  tartar 


Separation  of  Gold  and  Platinum.  283 

with  a  little  water,  drying  and  heating  them  till  the  mixture 
melts,  and  immersing  them  for  several  hours  in  diluted 
sulphuric  acid.  Heating  in  contact  with  fused  bisulphate  of 
potash,  or  with  powdered  sal-ammoniac,  is  also  employed  for 
the  same  purpose.  The  platinum  vessels  are  finally  well 
washed  with  water  and  burnished  with  agate. 

Platinum  is  sometimes  employed  for  the  touch-holes  of 
small-arms,  and  for  the  vents  of  cannon,  on  account  of  its 
resistance  to  corrosion.  The  circumstance  that  it  expands 
less  than  any  other  metal  when  heated,  enables  it  to  be 
cemented  into  glass,  by  fusing  the  latter,  whilst  other  metals ' 
which  differ  much  from  glass  in  their  rate  of  expansion  by 
heat,  would  crack  it  as  they  cool.  This  renders  platinum  of 
great  importance  in  the  fabrication  of  various  philosophical 
instruments. 

Though  pure  platinum  is  unaffected  by  nitric  acid,  it  may 
be  rendered  soluble  in  that  acid  by  previously  alloying  it 
with  ten  or  twelve  times  its  weight  of  silver,  which  is  taken 
advantage  of  in  order  to  separate  platinum  from  gold  in  the 
process  of  assaying  the  latter  metal  with  which  platinum  is 
frequently  associated.  If  the  platinum  be  present  in  small 
proportion  (not  exceeding  3  or  4  per  cent.)  in  the  alloy  of 
gold  and  silver  obtained  by  cupellation  (p.  255),  the  whole 
of  it  will  be  dissolved  together  with  tht  silver,  in  parting 
by  nitric  acid ;  but  when  the  quantity  of  platinum  is  larger, 
which  is  indicated  by  the  difficult  fusibility  of  the  button  on 
the  cupel,  and  by  the  blanched  appearance  of  the  gold 
eventually  obtained,  the  latter  must  be  again  fused  with  at 
least  three  times  its  weight  of  pure  silver,  the  alloy  rolled 
very  thin,  and  boiled  for  half  an  hour,  and  a  quarter  of  an 
hour,  respectively,  with  the  two  strengths  of  nitric  acid 
mentioned  at  page  255,  in  order  to  remove  the  whole  of  the 
silver  and  platinum.  An  alloy  of  silver  with  one-third  of  its 
weight  of  platinum  is  employed  by  dentists  on  account  of  its 
great  elasticity. 

The  remarkable  property  of  platinum,  especially  in  the 


284       Metals :  their  Properties  and  Treatment. 

finely-divided  states  of  spongy  platinum  and  platinum  black, 
to  condense  gases  into  its  pores  and  thus  to  promote  their 
chemical  action  upon  each  -other,  is  not  suited  for  descrip 
tion  in  a  metallurgic  treatise. 

PALLADIUM  is  generally  found  in  small  quantity,  not 
exceeding  i  per  cent,  associated  with  the  ore  of  platinum, 
from  which  it  is  extracted  by  a  process  which  is  purely 
chemical.  Formerly  there  existed  a  pretty  abundant  source 
of  this  metal  in  the  form  of  an  alloy  with  gold  found  in  the 
mines  of  Brazil,  but  of  late  years  this  has  failed,  and  pal 
ladium  has  risen  to  an  extremely  high  price.  In  appearance 
it  resembles  platinum,  but  is  much  harder,  though  it  pos 
sesses  considerable  malleability  and  ductility.  It  is  quite 
unchanged  by  air  at  the  ordinary  temperature,  but  assumes  a 
bluish  colour,  from  the  formation  of  a  thin  film  of  oxide,  at 
a  moderately  high  temperature,  becoming  bright  again  at  a 
higher  temperature,  the  oxide  being  decomposed.  Palladium 
fuses  at  a  somewhat  lower  temperature  than  platinum,  but 
cannot  be  fused  in  a  furnace.  It  is  only  half  as  heavy  as 
platinum,  its  specific  gravity  being  11-5,  so  that  it  is  much 
better  adapted  for  making  very  accurate  balances  and  other 
philosophical  apparatus.  The  graduated  scales  of  astro 
nomical  instruments  are  often  made  of  palladium,  and  an 
alloy  of  this  metal  with  -j^th  of  silver  has  been  sometimes 
employed  by  dentists. 


Ores  of  Antimony.  285 


ANTIMONY. 

Though  antimony  is  far  too  brittle  to  be  employed  in  its 
pure  state  for  any  useful  purpose,  it  has  been  shown  to  be 
of  great  service  in  hardening  the  softer  metals  lead  and  tin, 
so  that  the  history  of  this  metal  is  tfot  devoid  of  interest  for 
the  metallurgist. 

Antimony  is  occasionally  found  in  Nature  in  the  metallic 
state,  as  at  Andreasberg  in  the  Hartz,  where  it  is  alloyed 
with  small  quantities  of  silver,  iron,  and  arsenic.  The  only 
ore  from  which  it  is  largely  extracted  is  the  grey  antimony  ore, 
a  sulphuret  of  antimony,  containing,  when  pure,  7  if  parts  of 
antimony  combined  with  28^  parts  of  sulphur.  It  is  found 
in  Cornwall,  Auvergne,  Hungary  and  Borneo,  associated 
with  galena  and  iron  pyrites,  and  with  quartz  and  heavy 
spar,  in  veins  traversing  rocks  of  granite  or  slate.  The  ap 
pearance  of  grey  antimony  ore  is  very  characteristic ;  it 
commonly  resembles  a  compact  bundle  of  dark  grey  metallic 
needles  converging  towards  one  point,  and  often  exhibiting  a 
blue  iridescence  due  to  a  thin  film  of  oxide.  It  is  very 
heavy  (sp.  gr.  4-63),  and  melts  easily  even  in  the  flame  of  a 
candle.  This  fusibility  is  taken  advantage  of  in  order  to 
separate  it  from  the  earthy  matters,  to  effect  which  the  ore 
is  heated  on  the  concave  hearth  of  a  reverberatory  furnace, 
the  hearth  being  lined  with  charcoal  to  prevent  oxidation  of 
the  sulphuret,  which  melts  and  is  run  out  into  moulds, 
where  it  is  cast  into  the  form  of  the  cakes  sent  into  com 
merce  as  crude  antimony,  which  contains,  in  addition  to  the 
sulphuret  of  antimony,  sulphurets  of  arsenic,  iron  and  lead. 

The  oxide  of  antimony  occurs  in  Algeria,  and  is  smelted  in 
France. 

Red  antimony,  a  compound  of  oxide  and  sulphuret  of 
antimony,  is  found  in  Tuscany,  and  smelted  at  Marseilles. 


286       Metals:  their  Properties  and  Treatment. 

Regulus  of  antimony,  or  metallic  antimony,  is  extracted 
^from  the  sulphuret  by  melting  it  upon  the  hearth  of  a  rever- 
beratory  furnace  in  contact  with  metallic  iron  (clippings 
from  the  tin-plate  works),  which  removes  the  sulphur,  form 
ing  sulphuret  of  iron  ;  this  collects  above  the  melted 
antimony,  which  is  run  out  into  moulds.  It  contains  a  con 
siderable  quantity  of  iron. 

Sometimes  the  regulus  is  extracted  directly  from  the  rich 
antimony  ore,  without  previous  production  of  crude  anti 
mony.  For  this  purpose  the  ore  is  broken  into  pieces  as 
large  as  an  egg,  and  introduced  into  red-hot  crucibles, 
together  with  a  little  alkaline  slag ;  some  scrap-iron  is  placed 
on  the  top  and  pressed  down  when  the  mass  has  fused. 
After  about  two  hours,  the  melted  antimony  and  sulphuret 
of  iron  are  poured  into  conical  iron  moulds,  where  they 
separate  into  two  layers. 

A  purer  metal  is  obtained  by  the  following  process.  The 
sulphuret  of  antimony,  or  the  rich  original  ore,  is  crushed,  and 
roasted,  without  being  melted,  for  six  hours,  in  a  rever- 
beratory  furnace,  when  most  of  the  sulphur  is  expelled  as 
sulphurous  acid  gas,  and  most  of  the  arsenic  as  arsenious 
acid,  whilst  part  of  the  antimony  is  converted  into  vapour, 
and  combines  with  oxygen  to  form  the  oxide  of  antimony, 
which  is  carried  into  the  flues  of  the  furnace. 

The  roasted  ore,  which  has  a  red-brown  colour,  contains 
the  oxide  and  sulphuret  of  antimony.  It  is  ground  to 
powder,  mixed  with  about  one-fifth  of  its  weight  of  charcoal, 
some  chloride  of  sodium,  carbonate  of  soda,  sulphate  of 
soda,  and  slags  from  a  former  operation.  The  mixture  is 
thrown  upon  the  hearth  of  a  reverberatory  furnace,  and  well 
stirred,  when  the  oxide  of  antimony  in  the  roasted  ore  is 
reduced  to  the  metallic  state  by  the  charcoal,  whilst  the 
sulphuret  of  antimony  exchanges  its  sulphur  for  the  oxygen 
of  the  soda,  yielding  oxide  of  antimony,  which  is  also  reduced 
by  the  charcoal,  and  sulphuret  of  sodium,  which  forms  a  slag 
with  the  sulphurets  of  other  metals  present,  and  with  the 


Antimony.  287 

chloride  of  sodium.  The  metal  and  slag  are  run  off  into  an 
outer  basin. 

The  fumes  of  oxide  of  antimony  are  condensed  in  long 
flues.  The  poorer  ores,  after  being  roasted,  are  smelted  in 
cupola  furnaces  with  coke. 

The  antimony  is  refined  by  melting  it,  in  quantities  of 
60  or  70  Ibs.,  with  i  or  2  Ibs.  of  American  potashes  (car 
bonate  of  potash)  and  10  Ibs.  of  the  slag.  It  is  then  allowed 
to  solidify  quietly  under  a  layer  of  slag,  in  order  that  it  may 
assume  the  beautiful  fern-like  crystalline  markings  on  its 
surface  which  have  gained  for  it  the  name  of  star-antimony. 

The  above  process  for  extracting  the  metal  is  far  from 
economical,  little  more  than  one-half  of  the  antimony  present 
being  obtained  in  the  metallic  state. 

Antimony  can  easily  be  distinguished  from  ever)7  other 
metal  by  its  hardness,  brittleness  and  crystalline  structure  ; 
a  slight  tap  with  a  hammer  suffices  to  break  an  ingot  of 
antimony,  and  the  broken  surface  exhibits  large  shining 
plates  ;*  it  is  so  brittle  that  it  may  be  easily  reduced  to  a  fine 
powder  in  a  mortar.  It  is  comparatively  a  light  metal,  its 
specific  gravity  being  only  67.  It  melts  at  800°  F.,  and  at  a 
higher  temperature  it  gives  off  much  vapour,  which  produces 
a  thick  white  smoke  of  oxide  of  antimony.  Its  applications 
have  been  noticed  in  the  preceding  pages. 

*  The  addition  of  a  minute  proportion  of  tin  to  antimony  causes  it  to 
crystallise  more  readily  and  in  larger  crystals. 


288       Metals:  their  Properties  and  Treatment. 


BISMUTH. 

Bismuth,  or  marcasite*  as  it  was  formerly  termed,  is  a 
comparatively  rare  metal  which  is  found  associated  with  the 
ores  of  nickel,  cobalt,  copper  and  silver,  chiefly  in  Saxony, 
Transylvania  and  Bohemia.  It  also  occurs  in  smaller  quantity 
in  Cornwall,  Cumberland,  Stirlingshire,  Norway,  Sweden, 
and  the  United  States,  and  has  lately  been  found  in  Peru. 
Bismuth  is  always  extracted  from  the  ores  which  contain  it 


FIG.  105. — Extraction  of  Bismuth. 

in  the  uncombined  metallic  state,  by  taking  advantage  of 
the  readiness  with  which  it  fuses  (507°  F.)  and  drains  away 
from  the  other  constituents  of  the  ore.  It  is  extracted  chiefly 
at  Schneeberg  in  Saxony,  from  an  ore  containing  from  seven 
to  twelve  parts  of  bismuth  in  a  hundred,  associated  with  a 
compound  of  arsenic  and  cobalt.  This  is  broken  into  pieces 
about  the  size  of  a  nut,  and'  introduced,  in  charges  of  about 
5olbs.,  into  sloping  cast-iron  cylinders  (Fig.  105)  heated  by 
a  wood  fire.  The  lower  opening  (b)  of  each  cylinder  is 
closed  with  a  fire-clay  stopper  having  an  aperture  through 
which  the  melted  bismuth  may  run  out.  The  upper  open- 

*  A  term  sometimes  applied  also  to  iron  pyrites. 


Extraction  of  Bismuth.  289 

ings  are  closed  by  an  iron  door  (</);  in  about  ten  minutes 
after  charging,  the  metal  begins  to  run  into  an  iron  pot  (a) 
kept  hot  by  a  separate  fire  in  the  channel  (K),  and  containing 
a  little  coal-dust  to  prevent  the  oxidation  of  the  bismuth. 
The  ore  is  raked  about  occasionally,  to  promote  the  separa 
tion  of  the  metal,  which  is  exhausted  in  the  course  of  half 
an  hour,  when  the  residue  is  raked  out  from  the  upper  end 
of  the  cylinder,  where  it  falls,  down  an  incline,  into  a  trough 
of  water,  and  a  fresh  charge- is  introduced.  With  five 
cylinders  over  a  single  furnace,  one  ton  of  ore  is  smelted  in 
eight  hours.  The  iron  pans  are  emptied  into  moulds  in 
which  the  bismuth  is  cast  into  bars  weighing  from  25  to 
5olbs.  each. 

At  Joachimsthal,  the  bismuth  ores  have  of  late-  been 
smelted  in  crucibles,  by  melting  them  with  about  a  fourth  of 
their  weight  of  scrap-iron  (to  combine  with  the  sulphur),  half 
their  weight  of  carbonate  of  soda,  to  convert  the  silica  into 
a  slag  of  silicate  of  soda,  one-twentieth  of  lime  and  the  same 
weight  of  fluor  spar.  One  hundredweight  of  the  mixture  is  in 
troduced  into  each  crucible,  and  a  part  of  the  carbonate  of 
soda  is  employed  to  cover  the  mixture.  The  crucible  is  closed 
with  a  lid,  and  strongly  heated  in  a  furnace.  When  the 
mass  is  pasty  it  is  well  stirred  in  order  to  effect  perfect 
mixture,  and,  after  complete  fusion,  it  is  ladled  out  into 
conical  iron  moulds,  when  the  bismuth  subsides  into  the 
narrower  part  of  the  mould. 

As  it  comes  into  the  market,  bismuth  contains  considerable 
quantities  of  arsenic,  iron  and  silver,  which  do  not,  however 
seriously  interfere  with  its  limited  applications.  A  great 
part  of  the  arsenic  is  sometimes  expelled  by  heating  the 
metal  in  crucibles,  filled  up  with  charcoal  to  prevent  access 
of  oxygen,  when  the  arsenic  passes  off  in  vapour. 

When  a  sufficient  quantity  of  silver  is  present,  it  is  ex 
tracted  from  the  bismuth  by  the  process  of  cupellation 
(p.  208),  the  bismuth  becoming  converted  into  an  oxide 
which  is  removed,  like  the  litharge  formed  when  lead  is 


290      Metals:  their  Properties  and  Treatment. 

cupelled,  leaving  the  silver  upon  the  cupel.  It  is  stated 
that  the  great  rise  in  the  price  of  bismuth  during  the  last 
few  years  is  partly  due  to  the  circumstance  that  large  quan 
tities  of  it  have  been  bought  up  and  cupelled  for  the  sake  of 
the  silver  which  it  contains.  When  lead  containing  bismuth 
is  cupelled,  the  lead  is  first  converted  into  oxide,  so  that 
towards  the  end  of  the  process,  nearly  pure  bismuth  is  left 
on  the  cupel,  which  will  oxidise  in  its  turn  if  the  process  be 
continued. 

Bismuth  is  known  by  its  peculiar  reddish  colour  and  its 
highly  crystalline  appearance.  A  blow  with  the  hammer 
breaks  it  easily,  though  it  is  not  quite  so  brittle  as  antimony. 
Its  tendency  to  crystallise  is  very  remarkable;  by  melting 
some  bismuth  in  a  ladle,  allowing  a  solid  crust  to  form  upon 
•the  surface,  piercing  this  with  two  holes,  and  pouring  the 
liquid  bismuth  out  of  one  of  them  (the  other  allowing  the 
air  to  enter),  a  mass  of  beautiful  cubical  crystals  of  bismuth 
is  obtained. 

Its  brittleness  renders  bismuth  unfit  for  use  in  the  metallic 
state,  by  itself,  except  for  the  construction  of  thermo-electric 
piles,  which  are  made  of  alternate  bars  of  bismuth  and  anti 
mony,  and  are  employed  as  very  delicate  thermometers,  in 
order  to  measure  slight  differences  of  temperature  by  the 
electric  currents  which  they  produce. 

The  uses  of  bismuth  in  alloys  depend  upon  its  low  melt 
ing-point  (507°  K),  and  its  property  of  expanding  very  con 
siderably  during  solidification,  the  solid  metal  occupying 
-g^nd  more  space  than  the  liquid  metal,  affording  an  excep 
tion  to  the  general  law,  which  requires  that  cooling  should 
produce  contraction.  Another  remarkable  physical  pecu 
liarity  of  bismuth  is  the  circumstance  that  the  specific  gravity 
of  the  metal  is  diminished  instead  of  being  increased  by 
strong  pressure.  Thus,  a  cylinder  of  bismuth  of  specific 
gravity  9783  was  placed  in  a  steel  cylinder  fitted  with  a 
plunger,  and  subjected  to  a  pressure  of  200,000  Ibs.,  when 
its  specific  gravity  was  found  to  have  diminished  to  9*556, 


Sources  of  A  luminum.  2 9 1 

having  been  reduced  by  about  ^rd  part.     The  compressed 
bismuth  exhibited  scarcely  any  crystalline  structure. 

Newton's  fusible  alloy  is  composed  of  two  parts  of  bis 
muth,  one  of  lead,  and  one  of  tin,  and  melts  at  201°  F.,  so 
that  it  liquefies  readily  in  boiling  water,  although  the  most 
easily  fusible  of  its  constituents,  the  tin,  has  a  melting-point 
of  442°  F.  Such  an  alloy  is  used  as  a  soft  solder  by  pew- 
terers. 

^Some  kinds  of  type-metal  and  stereotype-metal  contain 
bismuth  in  order  that  they  may  expand  into  the  finest  lines 
of  the  mould  during  solidification.  For  a  similar  reason, 
an  alloy  of  tin,  lead,  and  bismuth  is  employed  for  testing 
the  finish  of  a  die. 

Bismuth  is  more  easily  converted  into  vapour  than  many 
other  metals,  and  may  be  boiled  at  a  moderate  white  heat. 


ALUMINUM. 

This  metal,  which  is  now  often  called  Aluminium,  al 
though  discovered  by  Wohler  in  1828,  has  only  within  the 
last  few  years  been  found  capable  of  useful  application  in  its 
metallic  form.  Though  never  found  as  a  metal  in  Nature,  it 
is  probably  the  most  abundant  of  all  metals  in  a  state  of 
combination,  since  it  exists  in  every  variety  of  clay  (silicate 
of  alumina),  its  quantity  varying  from  twelve  to  twenty  parts 
in  a  hundred.  Another  mineral  containing  aluminum  is" 
kryolite*  in  which  the  metal  is  combined  with  sodium  and 
fluorine,  and  forms  13  per  cent,  of  the  mineral,  which  is 
found  in  abundance  in  Greenland. 

*  So  called  from  the  Greek  for  frost  on  account  of  its  resemblance 

ir»A 


to  ice. 

U  2 


292       Metals :  their  Properties  and  Treatment. 

Aluminum  is  extracted  from  a  particular  variety  of  clay 
known  as  bauxite,  which  is  found  at  Baux,  near  Aries,  in  the 
south  of  France  ;  this  mineral  contains  about  one-third  of 
its  weight  of  aluminum,  combined  with  oxygen  (forming 
alumina],  together  with  silica,  oxide  of  iron,  and  water.  At 
Newcastle,  where  the  metal  is  extracted  from  bauxite,  the 
following  process  is  adopted  : 

The  ground  mineral  is  mixed  with  soda-ash  (containing 
carbonate  of  soda  and  caustic  soda)  and  heated  in  a  rever- 
beratory  furnace,  when  the  soda  combines  with  the  silica 
and  alumina,  forming  compounds  known  as  silicate  of  soda 
and  aluminate  of  soda,  whilst  the  carbonic  acid  is  expelled 
in  the  form  of  gas.  The  mass,  after  cooling,  is  treated  with 
water,  which  dissolves  the  aluminate  of  soda.  This  solution 
is  mixed  with  enough  hydrochloric  (muriatic)  acid  to  remove 
the  soda,  when  the  alumina  is  separated  as  a  gelatinous  pre 
cipitate  composed  of  hydrate  of  alumina,  a  compound  of 
alumina  with  water.  This  is  mixed  with  common  salt 
(chloride  of  sodium)  and  charcoal  powder,  to  a  stiff  paste, 
which  is  made  up  into  balls  as  large  as  an  orange,  very 
thoroughly  dried,  and  strongly  heated  in  earthen  cylinders 
through  which  perfectly  dry  chlorine  gas  is  passed. 

The  carbon  of  the  charcoal  combines  with  the  oxygen  of 
the  alumina,  escaping  as  carbonic  oxide  gas,  whilst  the 
aluminum  unites  with  the  chlorine  to  form  the  chloride  of 
aluminum;  the  latter  enters  into  combination  with  the 
chloride  of  sodium,  producing  a  double  chloride  of  aluminum 
and  sodium  which  distils  over  and  condenses  to  a  solid  salt. 
Ten  parts  of  this  salt  are  mixed  with  two  parts  of  sodium  in 
small  pieces,  and  with  five  parts  of  kryolite  or  of  fluor  spar, 
to  form  a  liquid  slag  which  shall  cover  the  surface  of  the 
metal.  This  mixture  is  thrown  upon  the  red  hot  hearth  of  a 
reverberatory  furnace,  which  is  then  immediately  closed  to 
exclude  air.  The  sodium  acts  violently  upon  the  chloride 
of  aluminum,  abstracting  its  chlorine  and  liberating  the 
aluminum,  which  collects,  in  the  melted  state,  beneath  a 


Aluminum.  293 

layer  of  slag  containing  the  chloride  of  sodium  and  kryolite. 
The  metal  thus  obtained  always  contains  silicon  and  iron  in 
considerable  quantity. 

Aluminum  is  a  white  malleable  metal  about  as  hard  as 
zinc,  and  fusing  at  a  somewhat  lower  temperature  than 
silver.  It  is  remarkably  light,  having  a  specific  gravity  of 
only  2*5,  and  is  unaffected  by  air  ;  unlike  silver,  it  is  not 
even  tarnished  by  air  containing  sulphuretted  hydrogen.  A 
bar  of  aluminum  suspended  from  a  string  sounds  like  a  bell 
when  lightly  struck.  In  manufacturing  objects  of  ornament 
from  aluminum,  a  solder  is  employed  which  contains  ninety 
parts  of  zinc,  six  parts  of  aluminum  and  four  parts  of 
copper. 

At  present,  the  principal  demand  for  aluminum  in  this 
country  is  for  the  manufacture  of  aluminum-bronze  or  alu 
minum-gold,  which  is  an  alloy  of  aluminum  with  nine  times 
its  weight  of  copper  (see  p.  175). 

An  alloy  of  silver  with  two-thirds  of  its  weight  of  aluminum 
is  used  in  France,  under  the  name  of  tiers-argent,  as  a  sub 
stitute  for  silver,  being  much  harder  than  that  metal  and 
less  than  half  the  price. 

Aluminum  is  sometimes  employed  for  making  small 
weights,  for  which  it  is  well  adapted  by  its  lightness  and 
resistance  to  the  action  of  air.  The  beams  of  small  balances 
have  also  been  made  of  aluminum. 


294       Metals :  their  Properties  and  Treatment. 


MAGNESIUM. 

Like  aluminum,  this  metal  has  only  been  extracted  in  any 
quantity  during  the  last  few  years,  a  considerable  demand 
for  it  having  arisen  in  consequence  of  its  property  of  burning 
with  a  very  brilliant  white  light  which  is  found  useful  for 
the  illumination  of  microscopes,  magic  lanterns,  &c.,  as 
well  as  for  taking  photographs  at  night  or  in  places  where 
daylight  does  not  penetrate. 

Magnesium  occurs  abundantly,  in  combination  with 
oxygen  and  carbonic  acid,  in  magnesite  (carbonate  of  mag 
nesia)  and  dolomite  or  magnesian  limestone  (carbonate  of 
lime  and  magnesia).  Another  source  of  the  metal  is  the 
recently-discovered  mineral  carnallite*  which  is  found  in 
large  quantity  above  the  rock-salt  in  the  salt  mines  of 
Stassfurth  in  Saxony.  This  mineral  is  composed  of  mag 
nesium,  potassium,  chlorine,  and  water,  and  contains  about 
one-twelfth  of  its  weight  of  magnesium.  The  water  may  be 
expelled  by  heat,  leaving  the  double  chloride  of  magnesium 
and  potassium. 

Magnesium  may  be  extracted  from  the  dried  carnallite  by 
mixing  it  with  one-tenth  of  its  weight  of  flu  or  spar,  to  act  as  a 
flux,  and  one-tenth  of  its  weight  of  sodium  in  small  pieces.  By 
fusing  this  at  a  moderate  heat,  the  chloride  of  magnesium  is 
made  to  give  up  its  chlorine  to  the  sodium,  and  the  mag 
nesium  collects  in  the  melted  state  beneath  a  liquid  slag 
composed  of  chloride  of  sodium,  chloride  of  potassium,  and 
fluoride  of  calcium.  The  magnesium  may  be  purified  by 
distilling  it,  in  an  iron  crucible,  as  practised  in  the  case  of 
zinc  (p.  156).  Magnesium  bears  considerable  resemblance 
to  aluminum,  but  is  a  whiter  metal,  and  even  lighter  than 

From  carnis,  Latin  for  flesh,  alluding  to  its  pink  colour. 


Sodium.  295 

aluminum,  its  specific  gravity  being  only  174.  It  may  be 
liquefied  below  a  red  heat,  and,  as  stated  above,  may  be 
readily  distilled.  It  is  a  little  more  tarnished  than  zinc 
when  exposed  to  air.  The  magnesium  wire  is  made  by 
forcing  the  heated  metal  through  holes  in  a  steel  plate,  and 
magnesium  riband,  by  passing  the  wire  between  heated 
rollers.  When  the  end  of  a  piece  of  wire  or  riband  is  held 
in  a  flame,  it  catches  fire  and  burns  with  a  dazzling  light, 
the  magnesium  combining  with  the  oxygen  of  the  air  to  form 
a  white  earthy  mass  of  magnesia. 

The  sodium  required  for  the  extraction  of  aluminum  and 
magnesium  is  extracted  directly  from  carbonate  of  soda, 
which  is  itself  made  from  common  salt  (chloride  of  sodium). 
The  well-dried  carbonate  of  soda  is  mixed  with  powdered 
charcoal,  some  chalk  being  added  to  prevent  the  fusion  of 
the  mixture,  which  is  strongly  heated  in  wrought-iron  cylin 
ders  protected  from  the  fire  by  a  coating  of  clay.  The  car 
bonate  of  soda  contains  sodium,  oxygen,  and  carbonic  acid ; 
the  carbon  of  the  charcoal  combines  with  the  oxygen,  and 
the  sodium  is  converted  into  vapour  and  condensed  in 
vessels  containing  petroleum  j  for  sodium  cannot  be  exposed 
to  the  air,  even  for  a  few  minutes,  without  combining  exten 
sively  with  oxygen,  and  it  even  takes  up  that  element,  with 
great  violence,  from  water,  in  which  the  oxygen  is  united 
with  hydrogen.  Sodium  would  scarcely  be  taken  for  a 
metal  by  an  ordinary  observer,  in  the  state  in  which  it  is  found 
in  commerce,  where  it  occurs  in  greyish  earthy -looking  light 
masses ;  but  when  these  are  cut  with  a  knife,  the  fresh  sur 
faces  exhibit  a  brilliant  lustre. 


296      Metals :  their  Properties  and  Treatment. 


CADMIUM* 

Cadmium  is  found,  in  small  quantities,  not  exceeding 
2  or  3  per  cent,  in  the  ores  of  zinc,  and  distils  over,  together 
with  the  first  portions  of  zinc,  during  the  smelting  of  the  ores 
of  that  metal,  the  period  of  its  distillation  being  known  as 
the  brown  blaze,  because  its  vapour  imparts  a  brown  colour  to 
the  flame.  If  these  first  portions  of  metal,  mixed  with  oxide, 
be  mixed  with  charcoal  and  distilled  again,  the  first  portions, 
being  collected  apart,  will  contain  a  still  larger  proportion  of 
cadmium,  this  metal  being  much  more  easily  converted  into 
vapour  than  zinc  is.  To  obtain  pure  cadmium,  the  mixture 
of  zinc  and  cadmium  is  dissolved  in  diluted  sulphuric  acid, 
and  sulphuretted  hydrogen  gas  is  conducted  into  the  solution, 
when  the  sulphur  combines  with  the  cadmium  to  form  a 
bright  yellow  sulphuret  of  cadmium  which  is  deposited. 
This  is  washed,  dissolved  in  strong  hydrochloric  acid,  and 
converted  into  carbonate  of  cadmium  by  adding  carbonate 
of  ammonia.  The  carbonate  of  cadmium  being  washed, 
dried,  and  distilled  with  charcoal,  as  in  the  case  of  zinc, 
yields  metallic  cadmium  in  a  pure  state. 

Cadmium  resembles  tin  in  colour  and  appearance,  as  well 
as  in  the  property  of  creaking  when  bent.  It  is  a  malleable 
and  ductile  metal  at  the  ordinary  temperature,  but  becomes 
brittle  at  about  180°  F.  It  melts  at  the  remarkably  low 
temperature  of  442°  F.,  the  melting-point  of  tin,  and  an  alloy 
of  three  parts  of  cadmium,  fifteen  of  bismuth,  eight  of  lead, 
and  four  of  tin  fuses  at  140°  F. 

Cadmium  is  harder  than  tin,  and  possesses  greater  tenacity. 
It  is  also  somewhat  heavier,  its  specific  gravity  being  8-6. 

*  From  cadmia  (Latin),  brass-ore,  referring  to  its  connexion  witli  the 
ores  of  zinc. 


INDEX. 


AIC                                               BAU                                              BRA 

AICH-METAL,  172 
Air,  action  of  upon 
heated  carbon,  31 

Antimony  —  cont, 
—  native,  285 
—  ore,  285 

Bean-shot  copper,  129 
Bell-metal,  4  copper,  i  tin, 

I  qo 

—  composition  of,  31 
Alloy,  fusible.  201 

All 

—  oxide,  285 
—  properties  of,  287 

Bessemer's  process,  62 
Bessemer  steel,  80 

Alloys,  149 
—  of  copper  and  tin,  149 
Alluvial  tin-ore,  131 

—  red,  285 
—  regulus,  286 
—  star-,  287 

-  —  tensile  strength  of,  89 
Bismuth,  extraction,  289 

Almaden,    extraction     of 

—  sulphuret,  285 

—  in  tin,  142 
Blackband,  17 

mercury  at,   262 
Altenau,  improvement  of 
lead  at,  194 
Altenberg  tin-works,  142 
Aludels,  264 
Aluminium,  291 
Aluminum,  291 
—  and  silver,  alloy,  293 

Apatite,  14 
Aquafortis  test  for  gold, 
253 
Argillaceous  iron-ores,  16 
Armour  plates,  71 
Arsenic,    no 
—  in  lead  shot,  202 
—  sulphuret,  203 

Black  copper,  118,  125 
refining  of,  125 
Black-jack,  153 
Black  plates,  145 
Blast-furnace,  20 
—  charging,  28 
—  chemical  changes  in,  30 
—  construction,  26 

—  -bronze,  175,  293 
—  extraction,  292 
gold,  293 

—  white,  no,  203 
—  pyrites,  104 
Arsenious  acid,  no,  203 

—  consumption  of,  48 
—  dimensions  of,  23 

Amalgam,  274 
—  dentists',  275 

Assay  of  gold  by  cupel- 
lation    254 

gases,  32 
—  lighting,  27 

—  for  electrical  machines, 

Augustus     process     for 

—  slag,  28 
—  tapping,  28 

275 
—  magnetic,  275 
—  of  gold,  243 

extracting  silver,  229 
Autogenous  soldering,  204 
Axes  tempered,  97 

Bleiberg,     extraction     of 
lead  at,  183 
Blende,  153 

—  of  silver,  221 
Amalgamating,  2 

Azurite,  105 

Blistered  copper,  119 
—  steel   64 

Amalgamation,  217 

Block  tin    140 

-  -floor,  218 
—  hot,  221 
—  Mexican  process,  218 
—  of  gold  ores,  243 
—  of  silver  ores,  217 
—  Saxon  process,  222 
Amalgams,  274 
Anglesea  copper,  128 
Anglesite,  177 
Annealing,  5 
—  steel,  94 
Anthracite,  109 
Antimony,  285 
—  alloy  of,  173 
—  and  lead,  alloy,  194 

BANCA  TIN,  140 
Bar-iron,  63 
—  best,  63 
—  casting  of,  63 
—  composition,  61 
—  consumption     of    coal 
for,  65 
—  crystalline,  66 
—  fibrous,  66 
—  manufacture,  48 
—  strength  of,  63 
—  working   strain   of,   71 
(note) 
Barometer,  273 
Barytes,  sulphate,  176 

—  plate,  140 
Bloodstone,  14 
Bloom,  56 
—  squeezers,  58 
Blowing-house,  141 
Blue  malachite,  105 
—  metal  (copper)  117 
—  steel,  98 
—  vitriol,  125 
—  water,  128 
Boiler-plate  iron,  64,  71 
Boiling  process  (iron),  55 
Boshes  of  blast-furnace,  22 
Bottoms  (copper),  117 
Brass,  168 

—  ~  crude,  285 
—  grey  ore  of,  285 
—  in  lead  ores,  183 

Bauxite,  292 
—  extraction    of    alumi 
num  from,  292 

—  for  engraving,  i7I 
—  founding,  169 
—  malleable,  172 

298 


Index. 


BRA                                             COP                                              COP 

Brass,  manufacture  of,  169 

Cast-iron  —  con  t. 

Copper  —  cont. 

Brazing,  206 

—  manufacture,  19 

—  antimony  in,  129 

Bright  iron,  39 

—  mottled,    40 

—  arsenic  in,  129 

Brightening,  211 

—  phosphorus  in,  41 

—  barilla,  103 

Britannia  metal,  152 

—  remelting  of,  46 

—  bean-shot,  129 

Bronze,  152 

—  silicon  in,  40 

—  best  selected,  117 

—  aluminium-,  175 

—  specific  gravity  of,  39 

—  bismuth  in,  129 

—  annealing  of,  152 

—  sulphur  in,  42 

—  blistered,  119 

—  coin,  95  copper,  4  tin, 

—  tensile  strength  of,  43 

—  cement,  128 

i  zinc,  152 

—  varieties  of,  42 

—  cleaned,  148 

—  founding,  152 

—  white,  39 

—  dry,  121 

—  nails,  152 

Cast-steel,  77 

—  effect  of  impurities  on, 

—  powder,  170 

Casting  iron,  46 

129 

—  pump-valves,  152 

Catalan  process,  100 

-  —  phosphorus  oil, 

—  sockets,  152 

Cawk,  176 

130 

—  stop-cocks,  152 

Cementation,  72 

sea-water  on,  130 

—  tempering  of,  152 

—  -furnace,  72 

—  electric     conductivity 

—  weapons,  152 

—  powder,  73 

of,  130 

—  wheel-boxes,  152 

—  theory  of,  74 

—  extraction  of,  106 

Bronzing,  171 

Cement  copper,  128 

atMansfeld,i22 

Brown  blaze,  158,  296 

Charcoal-plate,  144 

—  silver  from,  215 

—  haematite,  15 

refined  iron,  51 

—  feathered  shot,  129 

Browse,  186 

Chessy  copper,  iz8 

—  glance,  105 

Brunton's  calciner,  135 

Chill-casting,  39 

—  impurities  in,  129 

Brush-ore,  16 

Chilled  iron  softened,  39 

—  -indigo,  105 

Buddie,  134 

Chills,  39 

—  Lake  Superior,  103 

Bullets,  rifle,  201 

Chinese  cannon,  173 

—  lead  in,  122 

—  shrapnel,  202 

Chisels  tempered,  97 

—  moss,  118 

Burning-house,  134 

Cinder,  51 

—  native,  103 

Burra  Burra  copper,  130 

—  finery,  51 

—  nickel  in,  129 

Butter-milk  ore,  207 

—  from  blast-furnace,  35 

—  ore,  bituminous,  123 

Buttons,  gilding  of,  260 

iron,  46 

black,  105 

Cinnabar,  262 

—  —  grey>  ios 

to       J  )          J 

Clausthal,    extraction    of 

red,  105 

CAD  MI  A,  159 
Cadmium,  153,  296 

lead  at,  191 
Clay,  30,  291 

variegated,  104 
yellow,  104 

—  extracted    from    zinc- 

Clay  ironstones,  16 

—  ore  s,  104 

ores,  158 

Clinker,  109 

calcining  of,  107 

Calamine,  153,  154 

Coarse  copper,  118 

fusion    for    coarse- 

—  electric,  154 

—  metal,  in 

metal,  in 

Calciner,  108 

calcination  of,  116 

white-metal, 

Calcining,  19 

Coin-bronze,  152 

116 

furnaces,  20 

Coin,  gold,  252 

roasting,  107 

Calc-spar,  176 

—  silver,  232 

treated    for  silver, 

Calomel,  native,  262 

—  testing  of,  233 

2I5 

Cannon,  casting  of,  151 

Coins     of     copper     and 

—  overpoled,  121 

Carats,  253 

nickel,  175 

—  oxides  of,  104 

Carbon,    combustion    of, 

Coke-plate,  144 

—  oxygen  in,  121 

31 

Cold-blast  furnace,  25 

—  peacock-,  104 

—  in  iron,  37,  71 

Cold-short  iron,  69 

—  phosphorus  in,  130 

Carbonic  acid,  25 

Combined  carbon  in  iron, 

—  plates  cast,  128 

—  —  composition  of,  31 

37 

'  —  poling,  1  20 

—  oxide,  25 

Conducting  power,  7 

—  precipitated,  128 

composition  of,  31 

Converting  furnace,  72 

—  pyrites,  104 

Carnallite,  294 

Converting    vessel,    Bes- 

—  refining,  120 

Case-hardening,  98 

semer's,  80 

—      —  at  Mansfeld,  127 

Castilian  furnace  (lead), 

189 

Copper,  103 
—  alloys  of,  172 

—  rose,  128 
—  rosette,  126 

Cast-iron,  37 

—  and  arsenic,  130 

—  sand,  103 

—  classification  of,  43 

—  and  nickel,  174 

—  scale,  129 

—  composition  of,  42 
—  conversion  into  bar,  48 

—  and  silver,  232 
—  and  tin,  149 

—  schist,  123 
—  separated  from  silver, 

—  grey,  39 
—  malleable,  99 

—  and  zinc,  168 
—  Anglesea,  128 

215 
—  smelting,  107 

Index. 


299 


COP                                              GAL                                              GOL 

Copper  —  cont. 
—  smoke,  no 

Electric  calamine,  154 
—  conductivity  of  metals, 

Galena,  smelting  of,  178 
Gallery  furnace,  269 

—  Spanish,  130 

8 

Galvanised  iron,  167 

—  sulphate,  248 

Electro-gilding,  261 

Gangue,  35 

—  sulphur  in,  129 

Electro-magnets,  soft  iron 

Gases  from  blast-furnace, 

—  tin  in,  129 

for,  72 

34 

—  tinning  of,  148 

Electro-plating,  235 

Gas-furnace  for  puddling, 

—  tough-cake,  121 

Electro-silvering,  235 

63 

—  tough-pitch,  121 

Eliquation,  216 

Gedge's  metal,  172 

—  underpoled,  123 

Elongation  of  steel,  98 

German  silver,  173 

—  vessels  for  cooking,  148 

—  castings,  174 

Copperas,  128 

Gerstenhoffer's     furnace, 

—  blue,  248 

FAGOTTING        bar- 

in 

Cornette,  255 

iron,  64 

Gilder's  wax,    260 

Corrugated  iron,  168 
Coruscation,  211 

—  effect  of  repeated,  65 
—  theory  of,  66 

Gilding,  259 
—  dead,  260 

Cradle  for  gold-washing, 

Fahl-erz,  271 

—  electro-,  261 

242 

Fallow-ore,  271 

—  iron  and  steel,  261 

Crucible  of  blast-furnace, 

Fibre  in  iron,  66 

Gold,  239 

22 

—  destroyed     by    vibra 

—  alluvial,  240 

Crucibles    for     distilling 

tion,  67 

—  amalgam  of,  243,  259 

zinc,  156 

Fibrous  bar-iron,  66 

—  and  copper,  alloy  of, 

Crucibles      for      melting 

—  structure,  96 

252 

steel,  77 

Fine-metal  (copper),  117 

—  and     platinum     sepa 

Cryolite,  291 

—  iron,  51 

rated,  283 

Crystalline  iron,  67 

Finery-cinder,  51 

—  and    silver,   alloy    of, 

Cup  and  cone  for  blast 

—  furnace,  49 

206 

furnace,  33 

—  hearth,  49 

—  separated,  246 

Cupel,  208 
—  for  assaying,  254 

Fire-bridge,  53 
Flexibility  of  steel,  98 

—  assay  by  cupellation, 

254 

—  furnace,  255 

Floss-hole,  54 

beaters'  skin,  257 

Cupellation,  German  me 

Fluor-spar,  107,  176 

beating,  256 

thod,  213 

Flux,  28 

—  California!!,  252 

—  hot-blast,  215 

Forest  of  Dean  iron,  16 

—  carats,  253 

—  on  large  scale,  208 

Forge-iron,  29 

—  chloride  of,  260 

—  on  small  scale,  255 

Forging,    effect   of   upon 

—  cleaned  from  mercury, 

Cupola  furnace,  27,  46 

bar-iron,  67 

274 

Cyanide      of     potassium 

Fork    handles,    German 

—  coin,  252 

from  blast-furnace,  34 

silver,  174 

—  colouring  of,  256 

Cymbals,  150 

Forks,  German  silver,  174 

—  Dutch,  170 

Foundry-iron,  29 

—  effect  of  antimony  on, 

Fracture  of  bar-iron,  67 

252 

DAM-PLATE      of 
blast-furnace,  22 

Freiberg,    extraction     of 
silver  at,  222,  231 

lead  on,  252 
—  extracted   by  amalga 

Dam-stone    of   blast-fur 

Fuel  for  blast-furnace,  27 

mation,  243 

nace,  22 

Fulguration,  211 

—  —  from  old  silver,  246 

Dannemora  iron,  14 

Furnace,  blast,  20 

—  pyrites,  243 

Dead-head,  151 

—  calcining  (lead),  192 

quartz,  243 

Desilvering  lead,  194 

—  cementation,  -ji 

with  lead,  245 

Dolly,  134 

—  cupola,  46 

—  extraction  in  the  wet 

Dolomite,  294 

—  finery,  49 

way,  251 

Double  shear  steel,  77 

—  improving  (lead),  192 

—  fine,  252 

Doubles  (tin-plate),  148 

—  puddling,  52 

—  fineness  of,  expressed, 

Dowlais  foundry,  44 

—  regenerative,  10,  91 

253 

Ductility,  6 

—  re-heating,  64 

—  lace,  258 

Dutch  gold,  170 
—  metal,  170 

—  reverberatory,  52 
—  roasting,  108 

—  leaf,  256 
for  dentists,  256 

Fusibility,  9 

manufacture  of,  256 

Fusible  alloy,  291 

—  Mosaic,  171 

ECONOMICO-FUR- 

—  native,  240 

NACE,  189 

—  pens,  277 

Elasticity  of  steel,  70 

^ALENA,  175 

—  quartz,  240 

Elba  iron-ore,  15 

VJ  —  argentiferous,  176 

—  red,  260 

Electrical  amalgam,  275 

—  roasting  of,  177 

—  refining,  250 

300 


Index. 


GOL                                              IRQ                                              LEA 

Gold—  cant. 
—  removal     of   mercury 

Inquartation,  249 
Indium  and  osmium,  al 

JAPAN  copper,  128 

from,  274 

loy  of,  252,  277 

—  separated  from  silver 

Iron,  ii 

and  copper,  246 
—  standard,  252 
—  testing    of  with  aqua 

—  action  of  air  on,  49 
—  and  zinc,  alloy  of,  167 
—  bar-,  63 

KIEVE,  134 
Kirka'ldy's  experi 
ments,  95 

fortis,  253 

—  bright,  39 

Kish,  43 

—  —  —  touchstone,  254 
—  thread,  258 

—  carbide,  37 
—  carbonate,  16 

Knife-handles,      German 
silver,  174 

—  transparency  of,  258 

—  carburet,  37 

Knives  tempered,  97 

—  washing,  241 
—  white,  276 

—  cast,  37 
—  cold-short,  69 

Kongsberg,  treatment  of 
silver-ores  at,  217 

Gongs,  750 

—  combustion  of,  49,  82 

Krupp's  steel,  78 

Graphite  in  iron,  38 

—  corrugated,  168 

Kryolite,  291 

Green  malachite,  105 

—  direct  extraction    of, 

Grey  cast-iron,  39 

IOO 

theory     of     its 
production,  45 

—  districts,  48 
—  extraction  of,  18 

LACQUER,  171 
Lacquering,  171 

—  copper  ore,  105 

—  fibre  in,  55 

Lake  ores,  16 

—  forge-iron,  43 

—  galvanised,  167 

Lamination,  5 

—  slag,  186 

—  glance,  15 

Lancets  tempered,  97 

Guineas,  composition  of, 

—  grey,  39 

Lead,  175 

252 

—  homogeneous,  70,  90 

—  action  of  acids  on,  203 

Gun-metal,    10  copper,  i 

—  hot    and    cold     blast, 

—  and    antimony,    alloy 

tin,  150 

45 

of,  194 

Guns,  casting  of,  151 

—  hot-short,  69 

—  and  tin,  alloys  of,  204 

—  magnetic  oxide,  13 

—  argentiferous,  194 

—  malleable,   production 

—  calcining  of,  191 

HAEMATITE,  14 

of,  48 

—  carbonate,  176 

—  brown,  15 

—  meteoric,  12 

—  -coated  projectiles,  201 

—  red,  14 

—  mottled,  40 

—  containing  silver,  194 

Hammers,  steel  for,  70 

—  -moulders'  blacking,  48 

—  corrosion  of,  204 

Hammer  slag,  54 

—  native,  12 

—  desilverised,  194 

Hardening     by    chilling, 

—  ores,  12 

—  English,  191 

39,  70 

—  ore,  sparry,  16 

—  extraction       in       ore- 

•^i"    *  .. 

—  in  oil,  94 

—  phosphorus  in,  69 

hearth,  184 

—  steel,  94 

—  plates  cleaned,  145 

—  fume,  184 

Hard  metal,  151 

rolled,  145 

—  hard,  191 

Hearth  of  blast-furnace, 

—  pyrites,  18 

—  hardened,  201 

22 

—  red  oxide,  14 

—  improving  process,  191 

Heat,  bright  red,  10 

—  red-short,  69 

—  in  brass,  171 

—  cherry  red,  10 

—  refining,  49 

—  in  copper,  122 

—  conducting  power    of 

—  sand,  14 

—  native,  175 

metals  for,  7 

—  scales,  54 

—  -ore,    preparation    of, 

—  red,  10 

—  silicate,  49 

177 

—  white,  10 

—  smelting,  20 

—  ores,  175 

Heath's  process  (steel),  79 

—  specular,  82 

—  poisoning,  200 

Heaton's  process,  89 

—  steely,  70 

—  pressed,  183 

Heavy  spar,  176 

—  stones,  1  6 

—  silver  extracted  from, 

Heliotrope,  14 

—  sulphur  in,  69 

208 

Homogeneous  metal,  70, 

—  tinned,  144 

—  slags  smelted,  187 

90 

—  useful    properties     of, 

—  smelting,  177 

Horn  silver,  207 

IT 

—  smelting  in  Carinthia, 

Hornstone,  240 

—  variation    in  strength 

183 

Hot-blast,  25 

of,  65 

in    reverberatory, 

—  furnace,  25 

—  white,  39 

177 

—  iron,  45 

—  wire-,  64 

—  softening,  lyi 

Hot-short  iron,  69 

—  -works    of   the    Pyre 

—  Spanish,  191 

nees,  IOO 

—  sulphate,  177 

—  wrought,  63 

—  sulphide,  175 

IDRIA,    extraction    of 

—  —  direct  extraction  of, 

—  sulphuret,  175 

mercury  at,  265 
Indigo-copper,  105 

IOO 

manufacture  of,  18 

tin  pipes,  200 
—  uses  of,  200 

Index. 


301 


LEA                                               NOR                                             PLA 

Lead  —  cont. 

Mercury  —  cont. 

Noses  of  tuyeres,  37,  189 

—  virgin,  183 

—  impurities  in,  272 

Nova  Scotia  iron,  15 

•  —  white,  204 

—  nitrate,  259 

Nuggets,  gold,  239 

Leaden  chambers,  203 

—  properties  of,  273 

—  cisterns,  200 

—  purification  of,  272 

—  coffins,  204 
—  pipes,  200 

—  removal  from  gold,  274 
—  sulphide,  262 

OCHRES,  16 
Oil,  hardening  in, 

Lime  as  a  flux  for  iron 

—  sulphuret,  262 

94 

ores,  30 
—  composition  of,  35 

—  uses  of,  273 
Metal,i 

—  tempering  in,  97 
Oligist  iron  ore,  15 

—  use    in  the    blast-fur* 

Metallic  lustre,  2 

Oolitic  iron  ore,  18 

nace,  35 

Metals,  i 

Ore-furnace,  112 

Liquation,  215 

—  characteristics  of,  2 

slag,  115 

—  -hearth,  216 

—  conducting  power  for 

—  hearth,  184 

—  of  tin,  139 

electricity,  9 

Ores,  12 

List  on  tin-plate,  147 

—  ductility  of,  6 

Orpiment,  203 

-  -pot,  147 

—  fusibility  of,  9 

Osmiridium,  252 

Litharge,  210 
—  flaky,  215 

—  heat  conducted  by,  7 
—  malleability  of,  5 

Osmium      and      iridium, 
alloy  of,  252,  277 

—  green,  214 

—  specific  gravity  of,  7 

Oxyhydrogen  furnace,28o 

—  red,  214 

—  strength  of,  4 

—  reduction  of,  212 

Metal-slag,  in,  118 

Loadstone,  13 

Meteoric  iron,  12 

PADDLE,  54 

Lode,  14 

Meteorite  of  Lenarto,  12 

Paint,  metallic,  166 

Looking-glasses  silvered, 

Mexican  process  for  ex 

Palladium,  284 

274 
Lustre,  metallic,  2 

tracting  silver,  218 
Micaceous  iron  ore,  15 

—  and  silver,  alloy  of,  284 
Parting  of  gold  by  nitric 

Mild  steel,  70,  90 

acid,  249 

Mill  bar  iron,  63 

by  sulphuric  acid, 

MAGISTRAL,  219 
Magnesite,  294 

Mill-furnace,  64. 
Mine  iron,  46 

246 
Patera's  process  for  ex 

Magnesium,  294 

—  tin  ore,  131 

tracting  silver,  230 

—  extraction  of,  294 

Mirror  iron,  41,  84 

Pattinson's  process,  194 

—  properties  of,  294 

Mirrors,  manufacture  of, 

—  —  high  sj^stem,  198 

Magnetic  iron-ore,  13 

274 

low  system,  198 

Magnetite,  13 

Mispickel,  104 

Peacock  copper,  104 

Magnets,  steel  for,  71 

Moire  metallique,  148 

Pea  iron  ore,  15 

Malacca  tin,  140 

Mona  copper,  128 

Pencils,  metallic,  2qi 

Malachite,  105 

Mosaic  gold,  171 

Penknives  tempered,  97 

—  blue,  105 

Mottled  cast  iron,  40 

Pewter,  204 

Malleability,  5 

Muffle,  161,  255 

Phosphorus   in    bar-iron, 

Malleable  cast  iron,  99 

Muffle-furnace,  255 

69 

Manganese,      effect      on 

Mundic,  18 

—  iii   cast-iron,  41 

puddling,  61 

Muntz-metal,  172 

Pickling  iron  plates,  145 

—  in  cast  iron,  41 

Pig-boiling,  55 

—  in  iron  ores,  16 

Pig-iron,  28 

—  in  steel,  79 
Mansfeld  copper  process, 

-IVT  AILS,  bronze,  152 
-L  \    —  for  sheathing,  172 

Piling  bar-iron,  64 
Pimple  metal,  117 

122 

Nassau,  extraction  of  lead 

Pinchbeck,  171 

—  extraction  of  silver  at, 

in,  183 

Pins  tinned,  172 

215 
Marcasite,  288 
Market-pot  (lead),  195 

Native  copper,  103 
Nerve  in  iron,  66 
Newton's    fusible     alloy, 

—  whitened,  172 
Plane-irons  tempered,  97 
Plate-metal-,  51 

Matt,  113 
Melting-iron,  43 
Melting-points  of  metals, 

291 
Nickel,  173 
—  and  copper,  alloy  of, 

Plated  goods,    manufac 
ture  of,  234 
—  wire,  234 

10 

174 

Platina,  276 

Merchant  bar  iron,  63 

silver,  173 

—  muriate  of,  171 

Mercury,  259,  261 

—  speiss,  174 

Platinum,  276 

—  and  silver,  206 

Nitrate  of  soda  for  steel- 

—  ammonio-chloride,  277 

—  black,  269 

making,  90 

—  and    gold    separated, 

—  extracted    from    grey 

Nitrogen  in  steel,  89,  99 

283 

copper  ore,  271 

Northamptonshire      iron 

—  and  silver,  alloy  of,  283 

•  —  extraction  of,  262 

ore,  1  8 

—  black,  284 

302 


Index. 


PLA 

SIL 

SIL 

Platinum  —  cont. 

Rack,  134 

Silicon  in  iron,  40,  69 

—  cleaned,  282 

Rails,  Bessemer  steel,  S8 

—  in  steel,  89 

—  corroded,  282 

Railway  bars,  88 

Silver,  206 

—  crucibles,  281 

Rain-chamber,  185 

—  amalgam,  206,  221 

—  extraction  by  the  dry 

Ramrod  steel,  70 

—  and   aluminum,   alloy 

method,  279 

Razors  tempered,  97 

of,  293 

wet  method,  277 

Red  copper  ore,  105 

—  and  copper,    alloy  of, 

—  fusion  of,  278 

—  heat,  10 

232 

—  -iridium  alloy,  282 
—  nuggets  of,  276 

short  iron,  69 
steel,  93 

—  and  gold,  alloy  of,  206 
separation,  246 

—  ore,  276 

—  -shortness,  69 

—  and  mercury,  206 

—  soldering  of,  281 

—  silver  ore,  207 

—  and    palladium,  alloy 

—  spongy,  277 

—  zinc  ore,  153 

of,  284 

—  stills,  281 

Re?d  in  iron,  66 

—  and  platinum,  alloy  of, 

—  touch-holes,  283 

Refinery,  49 

283    \ 

—  uses,  281 
—  welding  of,  278 
Plattner's  process  for  ex 

slag  (copper),  122 
Refining  cast-iron,  49 
—  copper,  1  20 

—  applications  of,  232 
—  blackened  by  air,  233 
—  bromide,  207 

tracting  gold,  251 

Regenerative  stoves,  26 

—  chloride,  207 

Poling,  1  20 

Regulus,  113 

—  cleaned,  234 

Polishing,  3 

—  of  antimony,  286 

—  coin,  232 

Porter,  56 

Reverberatory     furnace, 

—  dead,  233 

Potash,      prussiate,     for 
case-hardening,  99 

52 
Richardson's         furnace 

—  extracted    by  Augns- 
tin's  process,  229 

Prince's  metal,  171 

(lead),  189 

by  Patera's  process, 

Proof-bar  (steel),  73 

Roaster-slag,  119 

230 

Proof  in  assaying,  255 
Prussiate    of    potash    for 

Roasting,  19 
furnace,  108 

by  Ziervogel's  pro 
cess,  230 

case-hardening,  99 

—  in  heaps,  19 

from  bismuth,  289 

Puddled     bar,     composi 

stalls,  124 

from  copper,  215 

tion,  61 

Rolling  iron,  57 

—  —  from  copper-matt, 

•  —  steel,  92 

—  metals,  5 

228 

Puddlers,  61 

Rolls,  chilled,  57 

from  copper  ores, 

Puddling,    disadvantages 

—  puddling-,  56 

215 

of,  61 

Rosette  copper,  126 

from  its  ores,  217 

—  dry,  55 

Rust,  protection  of  iron 

from  lead,  208 

—  fuel  required  in,  60 

from,  48 

—  extraction  by  amalga 

—  furnace,  52 

Rusting,  i 

mation,  217 

—  —  charge  of,  54 

by  lead,  217 

—  in  gas-furnace,  63 

—  fineness  of  expressed, 

—  loss  in,  60 
—  mechanical,  62 

SAL-AMMONIAC, 
148 

232 

—  frosted,  233 

—  process  of,  52 

Salmons  of  lead,  196 

—  German,  173 

—  rolls,  56 

Saws,  hardening  of,  94 

—  glance,  207 

—  superseded,  62 

Scaffolds,  27 

—  in  lead,  194 

Pyrenees,  iron-works  in, 

Schmollnitz  copper,  128 

—  in  lead-ore,  176 

100 

Schneider's  blast  furnace, 

—  iodide,  207 

Pyrites,  arsenical,  104 

34 

—  leaf,  237 

—  copper,  TOO 

Scoria,  122 

—  native,  206 

—  extraction    of     silver 

Scorification,  122 

—  ore,  brittle,  207 

from,  232 

Scotch   furnace  for  lead- 

red,  207 

—  iron,  1  8 

smelting,  184 

—  ores,  207 

Shear-steel,  77 

—  oxidised,  233 

QUARTATION,  249 

Shears  tempered,  97 
Shot,  202 
cast-steel,  88 

—  plate,  234 
—  refining,  215,  228 

,_J«.U*"*>  35'  1U/ 

•  —  gold  in,  240 

Siemens'  regenerative  fur 

—  solder,  206 

Quicklime  as  a  flux,  30 

nace,  10 

—  standard,  232 

Quicksilver,  261 

—  steel,  91 

—  sulphuret,  207 

Silica,  40,  107 

—  tarnished,  233 

—  composition  of,  40 

—  whitened,  233 

RABBLE,  54 
Rachette's     blast 

Silicate  of  iron,  52 
Silicium  in  iron,  40,  69 

Silvering,  235 
—  dry,  237 

furnace,  25 

—  in  steel,  89 

—  mirrors,   274 

Index. 


303 


SLA                                          TAP                                                   TIN 

Slag,  22                                    /     Star  antimony,  287 

Tap-hole,  23 

—  blast-furnace,  35 

Steel,  70 

Temper  of  steel,  94 

as  manure,  36 
—  —  composition,  36 

—  annealing  of,  94 
—  Bessemer,  80 

—  spoilt,  96 
Temperature  judged   by 

—  —  good  and  bad,  36 

—  blistered,  74 

colour,  10 

hearth,  187 

—  carbon  in,  70 

Tempering,  94 

—  in  bar-iron,  66 

—  cast,  77 

—  bronze,  152 

—  iron  refinery,  51 

—  colours  of,  97 

—  colours  in,  97 

.  lead,  189 

—  distinguished        from 

—  in  muffle,  98 

—  lead  furnace,  187 

iron,  94 

—  in  oil,  97 

—  metal-,  in,  118 

—  flexibility  of,  98 

—  steel,  94 

—  .ore-furnace,  115 
—  puddling-furnace,  60 
—  refinery  (copper),  122 

—  German,  92 
—  hardening  of,  94 
—  Heaton's,  89 

Temper-pot,  195 
Tenacity,  3 
—  effect  of  heat  on,  4 

—  roaster-,  119 

—  impurities  in,  92 

Tensile  strength   of  cast 

Slimes,  133 

—  Krupp's,  78 

iron,  43 

Smelting,  20 

—  magnetism  of,  70 

tested,  95 

—  -house,  137 

—  manufacture,  72 

Terne-plate,  206 

—  iron  ores,  20 

—  mild,  70,  90 

Test,  208 

Sodium,  295 

—  natural,  92 

Thermo-electric-piles,  290 

—  amalgam,  222,  275 

—  ore,  16,  92 

Thermometer,  mercurial, 

—  extraction  of,  295 
Soft  iron,  63 

—  polished,  3 
—  puddled,  92 

273 
Throat  of  blast-furnace,  22 

Solder,  205 

—  rails,  70,  88 

Tiers-argent,  293 

—  braziers',  206 

—  shear,  77 

Tile  copper,  117 

—  coarse,  205 

—  soft,  94 

Tilted  steel,  76 

—  common,  205 

—  tempering,  94 

Tilt-hammer,  76 

—  fine,  205 

—  tensile  strength  of,  95 

Tin,  130 

—  for  aluminium,  293 

—  tilted,  76 

—  alloys  of,  173 

—  pewterers',  205,  291 

—  toughened,  97 

—  amalgam  of,  274 

—  silver-,  206 

—  united  to  iron,  79 

—  and  copper,  alloys  of, 

Soldering,  205 

Steely  iron,  70 

149 

—  autogenous,  204 

Sterro-metal,  173 

—  and  lead,  alloys  of,  204 

—  hard,  205 

Straits  tin,  131 

—  Banca,  140 

—  use   of    sal-ammoniac 

Stream  tin  ore,  131 

—  black,  137 

in,  205 

Strength  of  iron  and  steel, 

—  block,  140 

Sovereign  gold,  253 
Sovereigns  tested,  253 
Spades,  steel  for,  70 

103 
—  of  metals,  3 
Sulphur  from  pyrites,  18 

—  boiling  of,  139 
—  casting  of,  141 
—  dropped,  140 

Spanish  copper,  130 

—  in  iron,  18,  42,  69 

—  foil,  144 

—  lead,  191 

—  in  steel,  93 

—  grain,  140 

Spathic  iron  ore,  16 

Sulphuric  acid  chambers, 

—  impurities  of,  139 

Specific  gravities  of  me 

203 

—  in  brass,  171 

tals,  6 

Sump,  166 

—  in  type-metal,  201 

—  gravity,  6 
—  —  -  determined,  233 

Sweating  furnace,  217 
Swedish  iron  ore,  14 

lead  pipes,  200 
—  liquation  of,  139 

Spectroscope    in     Besse- 

Sweep-washers,  248 

—  Malacca,  140 

mer's  process,  82 

Swords  tempered,  97 

ore,  130 

Specular  iron,  82 

calcining  of,  134 

—  —  ore,  15 

containing       tung 

Speculum-metal,  2  copper, 

'"T'ABLE  of  composition 

sten,  142 

i  tin,  150 

JL       of  cast  iron,  42 

dressing  of,  131 

Speiss,  174 

—  of  conducting  power, 

mechanical    prepa 

Spelter,  158 

8 

ration  of,  131 

Spence's  calciner,  no 
Spiegel-eisen,  41,  82 

—  of  copper  ores,  104 
—  of  ductility,  6 

prepared,  137 
roasting  of,  134 

Spongy  platinum,  277 

—  of     electric      conduc 

—  plate,  144 

Spoons,    German    silver, 

tivity,  9 

block,  140 

174 

—  of  fusibility,  10 

corrosion  of,  147 

Sprouting  of  silver,  281 

—  of  iron  ores,  31 

—  properties  of,  144 

Squeezers,  58 

—  of  malleability,  6 

—  refined,  140 

Stamp-chest,  132 
Stamping  from  puddling- 

—  of  specific  gravities,  7 
—  of  tenacity,  4 

—  refining,  139 
—  slags,  138 

furnace,  56 

Tap-cinder,  60 

—  smelting,  137 

304 


Index. 


TIN                                               ZIE                                                ZIN 

—  in  Saxony,  141 

T  TIMBERS,  16 

Zinc,  153 
—  action  of  air  on,  168 

—  stone,  130 

—  and  copper,  alloys  of, 

—  straits-,  131 
—  test  of  purity  of,  140 

VARNISHED    Steel, 
98 

1  68 
—  and     iron,    alloy    of, 

—  tossing  of,  140 
Tinned  iron,  144 

Vein-stone,  104 

167 
—  burned,  167 

Tinning  copper,  148 

Villacher  lead,  183 

—  carbonate,  153,  154 

•  —  iron,  146 
—  of  pins,  172 

Vitriol  chambers,  203 

—  chloride,  205 
—  combustibility  of,  167 

Titanic  acid,  14 

—  distilled,  154 

—  iron,  14 
Titanium,  14 

lyASH-  GILDING, 

—  dust,  164 
—  extraction,  154 

—  in  blast-furnace,  34 

Watch-springs  tempered, 

—  at  Bleiberg,  164 

—  steel,  89 
Tool  steel,  70 

97 
Weight  of  metals,  6 

at  Stolberg,  164 
at     Vieille      Mon- 

Tools  tempered,  97 

White  heat,  10 

tagne,  161 

Tossing,  140 

White  iron,  39 

Belgian  method,  159 

Tossing-tub,  134 
Touch-needles,  254 

—  —  theory    of  its   pro 
duction,  45 

English  method,  156 
Silesian  method,  161 

Touchstone,  254 
Tough-cake  copper,  120 

—  lead  ore,  175,  176 
—  metal,  118 

—  furnace,    Belgian-Sile- 
sian,  163 

Toughening  copper,  120 
Toughness  of  steel,  98 

for    electroplating, 
23S 

—  —  English,  157 
—  iron  in,  166 

Tough-pitch,  1  20 
Tungstate  of  baryta,  142 

Whitening  of  pins,  172 
Wire-drawing,  6 

—  lead  in,  166 
—  ores,  153 

—  soda,  142 
Tungsten,  131 

—  -iron,  64 
—  plated,  234 

calcination  of,  155 
treated  in  blast-fur 

—  in  steel,  72 

Wolfram,  131 

nace,  164 

Tungstic  acid,  131 

Working-pot,  195 

—  oxide  of,  153 

Tunnel-head,  22 

Wrought  iron,    manufac 

—  refined,  166 

hole,  22 

ture,  48 

—  removal  of  lead  from, 

Tuyere  pipes,  23 

166 

Tuyeres,  position  of,  44 
Twyers,  23 
Tymp-plate   of  blast-fur 

\7ELLOW    sheathing, 
I       172 

—  rolling  of,  165 
—  silicate  of,  154 
—  sulphide  of,  153 

nace,  22 

—  sulphuret  of,  153 

—  -stone  of  blast-furnace, 

yiERVOGEL'S      pro- 

—  uses  of,  1  66 

22 

£-s     cess    for    extracting 

—  white,  167 

Type-metal,  201 

silver,  230 

—  works,  154 

LONDON  :   PRINTED  BY 

Sl'OTTISWOODE    AND    CO.,     NEW-STREET    SQUARE 
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